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Mold Identification: 13 Types, Color Chart & Photos (2026)

Identify 13 common household molds by color, texture, and location. Mold identification chart, photo guide, and what looks like mold but isn't.

27 min read|0% complete|Published Dec 9, 2025 · Updated Aug 5, 2026

You spotted something fuzzy. It's on a wall, behind the sink, or on the ceiling, and now you're trying to figure out what it is before you decide what to do about it.

Good news: most mold you'll find in a house is ordinary and something you can handle yourself. Bad news: a small number of types are serious and shouldn't be touched without the right gear. This guide covers both, with photos, a color chart, and a section on the half-dozen things that look like mold but aren't.

Start Here: 60-Second Triage

Most people arrive at this page standing in front of the thing, phone in hand. Three questions, in this order.

1. Is it actually mold? Mold sits raised off the surface: fuzzy, velvety, or slimy. Dirt, soot, water stains, and efflorescence lie flat. Dab a drop of household bleach on the spot and wait two minutes. If it lightens, it's mold or mildew. If nothing changes, you're probably looking at one of the six lookalikes.

2. Is it the dangerous kind? Dark greenish-black, slimy when wet and powdery once dry, on drywall or ceiling tile that's been wet for days. Treat that as possible Stachybotrys, and don't touch it, wipe it, or point a fan at it. All three put spores in the air.

3. Do you clean it or call someone? Smaller than a sheet of paper, on a hard surface, with no musty smell elsewhere in the house: DIY is reasonable. Bigger than about 10 square feet, inside the HVAC, coming back after you clean it, or someone in the house has symptoms: bring in a professional.

Then match what you're seeing: black · green · white · pink · orange or yellow · brown or gray · side-by-side chart

In This Guide


Different types of mold growth on a residential wall showing black, green, and white mold patches
Mold on walls shows up in black, green, or white patches. Which kind it is changes how you deal with it.

What is Mold?

Mold is fungus. It's outside right now, on every fallen leaf and piece of dead wood within a hundred feet of you, and that's supposed to be there; that's its job. The problem starts when it finds its way inside, lands on something damp, and stays.

How Mold Spreads

Mold makes spores, which are small enough that you're breathing some in at this exact moment. Nothing to panic about; they're in the air everywhere, indoors and out. They only turn into a visible mold patch when they land somewhere wet and don't get dried out fast enough.

What Mold Needs to Grow

Mold needs four things. Take away any one of them and it can't grow.

Moisture. This is the one that matters. If your house is genuinely dry, you don't have a mold problem. Full stop.

Something to eat. Drywall, wood, paper, fabric, even the dust on the back of your TV. If you've got a house, you've got mold food.

A comfortable temperature. 60 to 80°F. The same range you're sleeping in.

Stagnant air. Basements, crawlspaces, that corner of the closet you never open, behind the couch that's been pushed against an exterior wall since you moved in.

Common Types of Household Mold

Close-up comparison showing different mold colors and textures including black, green, white, and pink varieties
Household molds look wildly different depending on species and growth stage. Knowing which is which tells you what you're dealing with.

Color and texture tell you a lot before anyone takes a sample. Here's what the most common household molds actually look like, and where they tend to show up.

The CDC lists the most common indoor molds as Cladosporium, Penicillium, and Aspergillus. All three are covered below, and none of them is Stachybotrys. That's worth holding onto before you assume the worst about a dark patch.

Black Mold (Stachybotrys chartarum)

Black mold (Stachybotrys chartarum) growing as dark greenish-black slimy patches on white drywall
Black mold (Stachybotrys) on drywall. Dark greenish-black, slimy texture, and the one that needs a professional.

This is the one people mean when they say "toxic black mold." Stachybotrys chartarum is the most concerning mold you're likely to find in a house, and it's the one you shouldn't try to clean yourself.

Warning: If you think you're looking at black mold, don't poke it, don't try to wipe it, and don't run a fan anywhere near it. All three aerosolize the spores. Call a mold assessor. That's the professional who tests, not treats, and they'll confirm what it actually is.

Black mold reads as dark greenish-black, slimy when it is actively growing and powdery when it dries, and it takes hold on cellulose like drywall, ceiling tiles, and wood that has stayed wet for days. Color alone cannot confirm the species, so treat any black patch as worth taking seriously and confirm with a test rather than by sight.

For the full visual breakdown, including what black mold actually looks like, surface by surface and how to tell it apart from soot, water stains, and other look-alikes, see the dedicated appearance guide.

Green Mold (Aspergillus and Penicillium)

Green mold (Aspergillus) growing as powdery green-teal fuzzy patches on a white wall
Green mold (Aspergillus). Powdery, fuzzy texture with lighter edges where it's actively spreading.

"Green mold" is usually Aspergillus or Penicillium. You've almost certainly met both already; Penicillium is the one behind blue cheese and penicillin. It runs from light green to dark olive, sometimes blue-green or yellow-green, powdery or fuzzy, with paler edges where it's actively spreading. You'll find it on food, on walls and insulation, in fabric and carpet, on wallpaper and painted surfaces, and cycling through the AC and ductwork (more on HVAC mold in the remediation guide). It spreads fast and covers ground quickly. Most strains are fairly harmless, but some set off allergies or breathing trouble, especially if you've already got asthma or hay fever.

White Mold

White mold growing as fluffy powdery patches on wood framing in a residential basement
White mold on basement wood framing. Often the earliest sign of a moisture problem.

"White mold" isn't one species. It's either a mold that stays white its whole life or one that hasn't turned green, gray, or black yet. Finding it early is the useful part; it's usually the first visible sign of a moisture problem. It shows up white to light gray, powdery or fluffy, sometimes with a faint musty smell, and on concrete it's easy to mistake for efflorescence (the mineral deposits left when water wicks through masonry). Look on basement walls and floors, around wood framing, in attics and crawl spaces, on furniture, and in closets that never get air. The tell is that it appears in humid spots with no obvious leak. If it's on your basement framing, something is keeping that wood damp even if you can't yet see what.

Pink Mold (Aureobasidium pullulans and Serratia marcescens)

Pink mold (Serratia marcescens) growing as pinkish-orange slimy spots on white bathroom tile grout
Pink mold in shower grout. Often actually bacteria (Serratia marcescens), common in bathrooms with standing water.

The pink ring in your shower isn't technically mold. Most of the time it's Serratia marcescens, a bacterium that feeds on soap scum and stays wet in the steam off your showerhead. It looks like mold, acts like mold, gets treated like mold, so people call it pink mold and move on. It's pink, orange, or reddish, slimy, usually in rings or spots, and it can darken toward brown or black as it ages. You'll see it on tile and grout, shower curtains and liners, around faucets and drains, on shampoo bottles and soap dishes, and on window sills in humid rooms. It lives on soap residue and standing water. It's not as serious as black mold, but for anyone with a compromised immune system it can cause real respiratory problems and infections, so don't wave it off just because it looks harmless.

Cladosporium

Cladosporium mold growing as olive-green to brown velvety spots on a residential window sill
Cladosporium on a window sill. Velvety texture, thrives near condensation. Common allergen and asthma trigger.

Cladosporium is the one you probably already have somewhere. It's among the most common molds in the world, indoors and out, with a trick most molds lack: it keeps growing in the cold, which is why it turns up inside refrigerators. Color runs olive-green to brown or black, the texture is suede-like or velvety, and it grows as clusters of small spots that spread outward, sometimes on both faces of a surface. Check window sills and frames, damp bathroom walls, HVAC ducts and air filters, fabric and carpet and upholstery, and under sinks around the plumbing. The standout trait is that cold tolerance, paired with being one of the top triggers for hay fever and asthma flare-ups. If allergy season feels worse inside your house than out, Cladosporium is a prime suspect.

Alternaria

Alternaria mold growing as dark brown-green velvety patches with fuzzy edges on a damp wall after water damage
Alternaria near a window after water damage. Fast-growing, strongly associated with allergic reactions.

Alternaria is the mold most responsible for household allergies. It hitches in on open windows, clothes, and pets, then settles wherever it finds damp, usually around condensation on windows or on a wall after a leak. It's dark brown to dark green or gray, velvety with hair-like filaments, and it spreads into large colonies with a distinctive fuzzy border. Look in showers and tubs and under leaking sinks, around window frames that sweat, in kitchens near the sink and dishwasher, on walls and ceilings after water damage, and inside AC systems. It's fast; it can take over a damp surface in a few days. It's strongly tied to allergic reactions and asthma attacks, and kids tend to react to it harder than adults do.

Chaetomium

Chaetomium mold growing as cottony white-gray to olive-brown fuzzy patches on water-damaged drywall
Chaetomium on water-damaged drywall. A strong sign of an ongoing moisture problem.

Chaetomium is the mold that tells you something's leaking before you've found the leak. See it and don't just clean it; track down the water, because it'll grow back until you do.

It starts white or gray and darkens to olive-green or brown as it ages, with a cottony, fuzzy texture and a strong musty odor, and it often shows up next to other water-damage molds like Stachybotrys. It favors water-damaged drywall and wallboard, roof leaks and the area around skylights, basement walls after a flood, plumbing leaks inside wall cavities, and wet cardboard or paper. The giveaway is the smell; people usually notice Chaetomium before they see it, and that musty odor is often the first sign of a hidden water problem.

Mucor

Mucor mold growing as thick white-grayish fluffy cotton-like patches near an HVAC vent
Mucor near an HVAC vent. Thick, fluffy growth that spreads fast in warm, humid conditions.

Mucor looks almost like a pile of wet cotton balls. It forms thick, fluffy patches that cover ground fast, especially near HVAC vents and anywhere condensation pools, and it shows up most in homes with inconsistent climate control. It's white or grayish, yellowing to brown with age, thick and cotton-like, growing in big patches rather than little spots and turning almost pillow-like when mature. You'll find it near HVAC systems and ducts, on carpet and padding, in condensation-prone spots like cold windows and uninsulated walls, around decaying organic material, and in the soil of an overwatered houseplant.

It grows fast in warm, humid air. For most households it's a nuisance, not an emergency; but in rare cases it causes mucormycosis, a serious infection that mainly hits people with weakened immune systems, so for anyone immunocompromised it's worth taking seriously.

Orange and Yellow Mold

Orange and yellow mold growing as bright slimy and crusty patches on wooden floor joists in a crawl space
Orange-yellow mold on crawl space wood. Sometimes slime mold (Fuligo septica). Always a sign of excess moisture.

Bright orange or yellow growth indoors is less common than black or green, and it isn't always true mold; some of what looks orange in a crawl space is actually slime mold, a different organism altogether. Either way it means moisture has gone on long enough to surface, so it's worth dealing with.

It comes in bright orange, yellow, or yellowish-green, sometimes slimy and wet or gelatinous, sometimes powdery or a bright crusty patch. Look on wood in crawl spaces and basements, around bathroom fixtures and tile, on food and in refrigerators, on mulch near entry points, and in HVAC condensation pans. If it turns out to be slime mold (Fuligo septica), it's technically a slime-forming protist, not a mold, but that doesn't change anything for you: find the water, dry it out, and remove the growth.

Brown and Gray Mold

Most of the time brown or gray mold isn't a separate species at all; it's one of the molds above in a different life stage. Mold shifts color as it matures, so a colony that started white can go green, then brown, then black over a few weeks. Expect anything from light tan to dark brown or silvery gray, in a texture that might be powdery, velvety, or slimy, usually in irregular patches that can read like a dark stain or old water damage. Treat it like any other mold: find the moisture source first, then deal with the growth. Color on its own doesn't tell you much.

Less Common Indoor Molds

The sections above cover most of what turns up in houses. A few others are genuinely indoor molds and worth being able to name.

MoldLooks likeWhere you'd find itWorth knowing
UlocladiumBlack to dark gray, suede-like, dense colonies that spread fastKitchens, bathrooms, basements, anywhere chronically wetRoutinely mistaken for Stachybotrys; only a lab tells them apart
AcremoniumMoist at first, then powdery; white, gray, orange, or pinkHumidifiers, cooling coils, drain pans, window sealantsLives in the wet parts of HVAC equipment
AureobasidiumPink or brown, darkening to black as it agesWindow frames, caulk, wallpaper, painted woodThe same organism named in the pink mold section above; listed again here because the pink stage is the one people recognize and the black stage is the one they misread as Stachybotrys
TrichodermaWhite with green patches, woollyDamp wood, wet carpet, HVAC filtersUsually turns up after flooding
FusariumPink, red, or purple, woollyWater-damaged carpet, humidifiersKeeps growing in cool conditions
SerpulaYellow-orange to red-brown, in wavy sheetsStructural timber, floors, beamsThis is dry rot, a structural problem more than a health one

One thing to skip past: you'll find Cryptococcus neoformans and Histoplasma capsulatum on plenty of "types of mold in your house" lists. They're soil organisms associated with bird and bat droppings. They matter if you're clearing out a pigeon-infested attic. They're not what's on your bathroom wall.

Mold Identification Chart

If you've got a spot and want to narrow it down fast, match what you're seeing against the table below.

Mold TypeColorTextureCommon LocationsRisk Level
Black mold (Stachybotrys)Dark greenish-blackSlimy when wet, powdery when dryChronically wet drywall, ceiling tiles, behind wallpaperHigh; call a pro
Green mold (Aspergillus/Penicillium)Light to dark green, blue-greenPowdery or fuzzyFood, HVAC systems, walls, carpetsModerate; can cause allergic reactions
White moldWhite to light grayPowdery or fluffyBasements, attics, crawl spaces, wood framingModerate; early sign of moisture problems
Pink mold (Aureobasidium/Serratia)Pink, orange, reddishSlimyBathroom tiles, grout, shower curtains, drainsLow to moderate; infections in immunocompromised
CladosporiumOlive-green to brown or blackVelvety or suede-likeWindow sills, HVAC ducts, fabrics, damp bathroomsModerate; common allergen and asthma trigger
AlternariaDark brown to dark greenVelvety with hair-like filamentsShowers, sinks, window frames, after water damageModerate to high; strong allergen, fast grower
ChaetomiumWhite to olive green (darkens with age)Cottony or fuzzyWater-damaged drywall, roof leaks, basement wallsModerate; strong sign of water damage
MucorWhite to grayish, yellows with ageThick, fluffy, cotton-likeHVAC systems, carpet, condensation areasModerate to high; can cause mucormycosis in immunocompromised

One note: Color alone isn't a reliable way to pin down the exact species. Molds shift colors as they age, and the only way to know for sure is lab testing. When you need certainty, get a professional mold assessment.

Mold vs Mildew (Quick Summary)

Side-by-side comparison showing dark fuzzy mold growth versus flat powdery mildew on household surfaces
Mold (left) grows into surfaces and has a fuzzy texture. Mildew (right) sits flat on the surface and wipes off easily.

People use "mold" and "mildew" interchangeably, but they aren't quite the same. Both are fungi, and mildew is really a flat, surface-level form of mold: white or gray, powdery, and easy to wipe off a hard surface. What people call mold is the fuzzy, raised growth that roots into drywall, wood, and ceilings and usually needs more than a wipe.

The shortcut: mildew sits on top. Mold goes in. If it's raised, fuzzy, or dark, treat it as mold. You can always downgrade your concern later if it turns out to be mildew, but it's harder to undo the other direction.

For the side-by-side table on color, texture, smell, and health risk, plus a simple at-home test and surface-by-surface guidance, see the full mold vs mildew breakdown.

What Looks Like Mold But Isn't

A handful of ordinary household things get mistaken for mold all the time. Match what you're seeing against the six below before you start pulling anything apart.

Before you start pulling off drywall, check whether you’re actually looking at mold.

Efflorescence

Mineral salts carried to the surface as water evaporates through masonry. Most "white mold in the basement" is this.

The test

Dissolves in water. Mold doesn’t.

Dirt and soot

Dark buildup near vents, windows, and high-traffic spots.

The test

Feels gritty and lies flat. Mold is raised.

Soap scum

White to gray film on bathroom surfaces.

The test

Wipes off easily, and there’s no musty smell.

Water stains

Brown or yellowish rings left by an old leak.

The test

Flat discoloration, not raised growth. Still worth chasing the moisture.

Iron bacteria

Rust-colored staining from iron-oxidizing bacteria in the water supply.

The test

Shows up around drains, toilets, and fixtures, not on walls.

Pollen

Fine yellow-green powder during allergy season.

The test

Wipes away and stays gone, unless more blows in.

Still not sure? The bleach test settles most of these. Dab a drop on the spot; if it lightens within two minutes, it’s mold or mildew.

Two of these are worth a second note. A water stain still means a moisture problem that will grow mold if you ignore it, so don't dismiss it just because it isn't mold yet; and if what's on the ceiling is raised and fuzzy rather than flat, that's what mold on a ceiling actually means. Efflorescence is the opposite case: fix the moisture and it's gone for good.

How to Tell the Difference

The bleach test is the fastest way to rule things in or out. Dab a drop of household bleach on the suspicious spot. If it lightens within one or two minutes, you're looking at mold or mildew. Dirt, efflorescence, and mineral deposits won't change color.

Other signs it's mold and not a lookalike:

  • Fuzzy, slimy, or raised texture
  • Musty or earthy smell in the area
  • The discoloration keeps coming back after you clean it
  • The spot has a history of moisture problems or past water damage

When the bleach test is inconclusive and the smell test isn't giving you much, a professional mold assessor can take samples and give you a definitive answer.

Where Mold Commonly Grows

If you're trying to track down where mold is likely to be hiding, start with the places that stay damp the longest.

High-Risk Areas

Hidden Locations

Professional mold assessor revealing hidden mold growth behind drywall during an inspection
Hidden mold behind drywall turns up regularly during professional inspections. Musty odors and water stains are the key warning signs.

A lot of mold grows where you can't see it:

  • Behind drywall and wallpaper
  • Inside HVAC ducts and systems
  • Under carpeting and padding
  • Behind cabinets and furniture
  • Inside wall cavities around plumbing
  • Beneath flooring materials

Signs of Hidden Mold

You can't see it, but these are the signs it's there:

  1. Persistent musty or earthy odors
  2. Visible water stains on walls or ceilings
  3. Peeling or bubbling paint or wallpaper
  4. Warped or buckled flooring
  5. Chronic allergy symptoms that improve when away from home

Health Risks Associated with Mold

How mold affects you depends on three things: how sensitive you are, how much exposure you've had, and which mold it is. For a fuller breakdown of symptoms by mold type, short-term vs. long-term effects, and when a doctor visit is warranted, see our mold exposure symptoms guide.

Common Symptoms of Mold Exposure

Most people get mild symptoms:

  • Nasal congestion and runny nose
  • Sneezing
  • Eye irritation (redness, itching, watering)
  • Skin rashes or irritation
  • Throat irritation
  • Coughing
  • Headaches

More Serious Reactions

Some people get hit harder:

  • Difficulty breathing or shortness of breath
  • Fever
  • Chronic fatigue
  • Memory problems or difficulty concentrating
  • Persistent sinus infections

If you're in a high-risk group (compromised immune system, chronic respiratory condition, severe allergies, or asthma), you're at much higher risk from mold exposure. Don't try to handle anything beyond a small patch yourself, and see a doctor if symptoms develop.

When to Call a Professional

A patch under 10 square feet is usually something you can handle yourself. Bigger than that, or in the situations below, you need a pro. Not sure which side of the line you're on? DIY vs. professional removal →

How Big Is Too Big?

Ten square feet is hard to picture when you're staring at a wall. Here's the same threshold in things you already have around the house, drawn to scale.

  1. Index card
    3 × 5 in

    Scattered spots and speckles on a hard surface

    Wipe it down, fix the humidity, keep an eye on the spot

  2. Sheet of paper
    8.5 × 11 in

    A single patch

    DIY with gloves, an N95, and the windows open

  3. Door
    36 × 80 in

    A wall section

    The upper limit of DIY; get advice before you start

  4. Larger than a door
    over 10 sq ft

    Over 10 square feet, or spread across several surfaces

    Professional containment, not a spray bottle

Square footage isn't the only trigger, though. The situations below call for a professional at any size.

Call a Professional Immediately If:

  1. The patch is bigger than 10 square feet. Larger growth needs professional containment, not a spray bottle.
  2. You think it's black mold. The health risk is too high to gamble on a DIY cleanup.
  3. It's in your HVAC system. The ducts will carry spores into every room.
  4. There's been sewage backup or contaminated water. That stacks a category of health hazard on top of the mold.
  5. It keeps coming back after you clean it. Something is still feeding it with moisture.
  6. Someone in the house has symptoms, especially respiratory ones.
  7. You can smell it but can't find it. Hidden mold takes professional detection to locate.

When you're not sure, call someone. A professional mold assessment is affordable and it's a lot cheaper than the health or property damage that comes from guessing wrong.

What a Professional Assessment Actually Involves

A certified mold assessor will:

  1. Conduct a thorough visual inspection
  2. Use moisture meters to detect hidden water issues
  3. Collect air and/or surface samples if needed
  4. Identify the moisture source causing the problem
  5. Provide a detailed report with remediation recommendations

Choosing the Right Professional

Here's what to look for:

  • State licensing (required for mold assessors in many states)
  • Current insurance coverage
  • Verifiable certifications from recognized organizations like IICRC
  • Detailed written assessments, not just verbal opinions
  • No conflict of interest. The assessor shouldn't also be doing the remediation (here's why that matters)

For the full process, see our hiring guide, along with questions to ask and scams to avoid.

How to Identify Mold in Your House

Mold identification comes down to three things: what it looks like, where it's growing, and whether it passes a simple test.

Visual clues:

  • Fuzzy or slimy texture. Mold is raised from the surface; dirt and stains lie flat.
  • Irregular patches. Mold spreads outward from a moisture source in organic, splotchy patterns.
  • Color. Green, black, white, brown, orange, or gray. Use the chart above to narrow it down.
  • Growth pattern. Mold follows water. If the discoloration is clustered around pipes, windows, HVAC vents, or old water stains, you're probably looking at mold.

The bleach test. Dab a drop of household bleach on the spot. If it lightens within 1–2 minutes, it's mold or mildew. Dirt and mineral deposits won't change color.

The smell test. Mold has a distinctive musty, earthy odor. If a room smells damp even after you've cleaned it, there's probably hidden mold behind a wall, under flooring, or in a ceiling cavity. For a fuller breakdown, including what different molds smell like and the everyday odors people mistake for mold, see what mold smells like.

When you still can't tell. A professional mold assessor has moisture meters, thermal imaging, and air sampling that can confirm what's there and what species it is. That's when it's time to bring one in.

Is There an App That Can Identify Mold?

Yes, more than a dozen of them, and most arrived in the last year or so. Point your phone at a patch and you get back a species name and a confidence score.

Read their own documentation and the picture gets clearer. Mold Scanner AI's methodology page describes what it does as "AI-assisted visual screening," and states plainly that a screening label is not confirmation that mold is present or active, that the tool does not determine species or active growth, and that dirt, shadows, mineral deposits, and water marks can all look alike in a photograph. It tells you to consult a licensed or certified inspector for anything that matters.

That's an honest description, and it points straight at the real limit. The ceiling here isn't the app. It's the photograph.

  • The answer isn't in the picture. Aspergillus, Penicillium, and Cladosporium all present as green. Stachybotrys, Cladosporium, and Ulocladium all present as black. A trained assessor standing in the room can't separate those by eye either. A camera has strictly less to work with than the assessor does, and better software can't add information the photo never captured.
  • A photo only shows the surface. What's on the drywall is the symptom. The moisture behind it is the problem, and nothing you can photograph will show you that.

The apps say as much in their own disclaimers, which describe results as estimates rather than diagnoses. That's accurate, and it's the part people scroll past.

Before you pay for one, try the same photo in a general AI assistant you already have on your phone. You'll get the same kind of answer: a reasonable read on color and texture, and no way to confirm a species.

So ask a different question. Which tool you use matters far less than what you ask it:

  • "What kind of mold is this?" Nothing answers this from a photo. Not the app, not a general AI assistant, not a professional looking at the same image.
  • "Is this raised and fuzzy, or is it flat?" Any of them handles that fine, and it's the question that actually decides what you do next.

One boundary to hold onto: use these tools to rule something in, never to rule it out. If a model looks at your wall and says that looks like mold, believe it and deal with it. If it says probably nothing, that isn't an all-clear. It hasn't seen behind the drywall, and it can't tell Stachybotrys from Cladosporium any better than you can.

Are DIY Mold Test Kits Worth It?

Usually not, and the reasons are specific.

The settling-plate kits sold in hardware stores work by leaving a petri dish open in a room and seeing what grows on it. Something almost always grows, because mold spores are in the air of every building on earth. A positive result mostly confirms that you live indoors.

From there the problems stack up:

  1. No baseline. Without a matched outdoor sample taken at the same time, an indoor spore count has nothing to be compared against, so the number on its own means very little.
  2. It only grows what's still alive. Dead spores still trigger allergic reactions, and a culture plate won't show them at all.
  3. No accredited lab, no chain of custody. Results without documented handling from an accredited lab carry little evidentiary weight, which matters if you're building an insurance claim, a landlord dispute, or a disclosure before a sale.
  4. Sampling stirs it up. Taking your own surface sample means agitating the colony, and a dust mask isn't adequate protection for your eyes, skin, and airways.

The CDC goes further than we would: it doesn't recommend mold testing at all, on the reasoning that you don't need to know the species to know you need to remove it. For most household situations that's right. Testing earns its cost when you need documentation for somebody else: an insurer, a landlord, a buyer, or a doctor.


Next Steps

If you're pretty sure you've got mold, here's the order of operations:

  1. Document what you see. Photos and measurements of the affected area.
  2. Find and fix the moisture source. Mold can't survive without water. If you don't fix the leak, nothing else matters.
  3. Don't disturb it. Poking, wiping, or fanning mold aerosolizes the spores.
  4. Measure the patch. Under or over 10 square feet?
  5. Decide your approach. DIY for small patches of common mold. Professional for anything larger, any suspected black mold, or anything in an HVAC system.

Mold remediation cost guide →

Find a Verified Mold Professional

Your home and your health are both on the line, so don't hire the first name that shows up. Find a verified mold inspection company in your area. Every professional we list has been vetted for proper licensing, insurance, and reputation.

📚 This guide is part of our Complete Mold Remediation Guide. Your full resource for understanding, preventing, and removing mold.

Frequently Asked Questions

What does mold look like on walls?
On walls, mold usually shows up as fuzzy or slimy patches in dark colors: black, green, brown, or gray. The mold on walls guide covers what each growth pattern means and how to fix it.
How can you tell the difference between mold and mildew?
Mildew sits on top; mold goes in. Mildew is flat, powdery, and usually white or gray, and it wipes off a hard surface with household cleaner. Mold is fuzzy or slimy, raised off the surface, usually dark (black, green, or brown), and it roots into the material, which is what makes it harder to remove.
Is all black mold toxic?
No. 'Toxic black mold' specifically means Stachybotrys chartarum, which produces mycotoxins. Plenty of common molds look dark or black but are less dangerous species like Cladosporium or Alternaria. Color can't tell them apart; only lab testing confirms the species. So treat any black patch with caution and get a professional to confirm what it actually is.
Can mold be hidden behind walls?
Yes, and often. It grows behind drywall, under flooring, and inside wall cavities wherever moisture collects out of sight. The mold on walls guide covers the signs mold is inside a wall and how pros confirm it.
What does mold smell like?
Musty, earthy, damp. Most people land on wet socks, rotting wood, or an old basement. That smell is microbial volatile organic compounds (MVOCs), gases mold gives off as it grows. A musty smell that won't clear no matter how much you clean is one of the strongest signs of hidden mold.
How quickly should you address mold in your home?
As soon as you find it. In the right conditions mold can double within 24 to 48 hours, so waiting only makes it bigger and more expensive to fix. A small patch (under 10 square feet) is usually a DIY job; anything larger needs professional remediation.
What does early stage mold look like?
Tiny dark specks or a faint discoloration, easy to mistake for a smudge of dirt or a light stain. In bathrooms it's the small black or green dots along grout lines and caulk; on walls it's a barely-there cluster of spots. This is the easiest stage to deal with. Catch it under 10 square feet and DIY cleaning usually does the job.
How can you tell if it's mold or dirt?
Run the bleach test: dab a drop of household bleach on the spot, and if it lightens within a minute or two, you're looking at mold or mildew. Dirt won't change color. Texture helps too; mold is slightly fuzzy or raised, dirt is flat and gritty. And if the spot keeps coming back after you clean it, it's almost certainly mold with a moisture source feeding it.
Can mold grow on concrete?
It can, but not on the concrete itself; it feeds on the dust, dirt, and organic film that settle on top. Basement walls and floors are common spots thanks to humidity and condensation. One catch: white powdery deposits on concrete are often efflorescence (mineral salts), not mold. The quick test is water; efflorescence dissolves, mold doesn't.
What color mold is the most dangerous?
Color won't tell you. Black mold (Stachybotrys chartarum) gets named most often because it produces mycotoxins, but plenty of black-colored mold isn't Stachybotrys at all, and green, white, even pink molds can cause problems depending on the species and how sensitive you are. The only way to know the species is lab testing. If any mold in your home worries you, have a mold assessor take a look.
What is the most common mold in a house?
The CDC lists the most common indoor molds as Cladosporium, Penicillium, and Aspergillus. Cladosporium is the one most households already have somewhere; it grows on window sills, fabric, and painted surfaces, and unusually for a mold it keeps growing in the cold, which is why it turns up inside refrigerators. None of the three is Stachybotrys.
Is there an app that can identify mold from a photo?
There are more than a dozen, and their own documentation is the best guide to what they can do. Mold Scanner AI's methodology page calls it 'AI-assisted visual screening' and says outright that the tool does not determine species and that a screening label is not confirmation mold is present. The ceiling isn't the software, it's the photograph: Aspergillus, Penicillium, and Cladosporium all look green, and Stachybotrys, Cladosporium, and Ulocladium all look black. A trained assessor standing in the room can't separate those by eye either. Use any of these tools to rule mold in, never to rule it out.

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This guide is for educational purposes only. Always consult with certified professionals for specific mold situations in your home. If you experience health symptoms, please consult a healthcare provider.