Los Angeles County · Renter guide
How to Check and Test for Mold in Your Apartment
To check an apartment for mold, use your eyes and nose first: look under sinks, around windows, on bathroom ceilings and in closets on outside walls. Track humidity with a hygrometer, photograph everything with dates, and skip the cheap settle-plate kit. Call the city or a lab tester when the cause is hidden.
- Cost to checkFree, with a phone camera
- ToolsFlashlight and a hygrometer
- CoverageAll of Los Angeles County
- StandardEPA and CDC guidance
- Call(213) 659-0672
Signs and smells
What are the signs of mold in an apartment?
The most reliable signs are spots that grow or come back after cleaning, a musty smell that’s stronger in one room, and water stains, bubbling paint or soft drywall. Mold can be black, green, gray, white or orange. Color doesn’t tell you how serious it is; moisture does.
- Spots that return: clusters of dots or fuzzy patches that come back within weeks of wiping.
- Stains and paint damage: yellow or brown rings on the ceiling, peeling or bubbling paint, warped baseboards.
- Soft or swollen materials: drywall that gives when you press it, or cabinet floors that are warped under the sink.
- Symptoms that ease when you leave: stuffiness or coughing that improves away from home is worth mentioning to your doctor.
What does mold smell like?
Mold usually smells musty and earthy, like a damp basement, wet cardboard or old books. The odor comes from gases that growing mold releases, called MVOCs. A strong smell with nothing visible often means mold inside a wall, under flooring or in an air duct.
Room by room
Where should I look for mold in an apartment?
Look wherever water collects or air doesn’t move: under sinks, around the toilet and tub, on bathroom ceilings, along window frames, in closets on exterior walls, and behind furniture pushed against outside walls. In older LA buildings, also check below any upstairs bathroom and around the water heater.
| Where to look | Why mold grows there | What to check |
|---|---|---|
| Under kitchen and bathroom sinks | Slow drips from drains and supply lines | Cabinet floor, back wall, the pipes themselves |
| Bathroom ceiling and upper walls | Shower steam, often no working exhaust fan | Corners above the shower, around the light fixture |
| Window frames and sills | Condensation, rain getting past old seals | Sill corners, the bottom of curtains and blinds |
| Closets on outside walls | Cool walls and still air | Back wall near the floor, stored shoes and boxes |
| Behind beds, dressers and couches | Furniture traps moist air against cool walls | Pull items a few inches out and use a flashlight |
| Ceilings below an upstairs unit | A neighbor’s shower, toilet or washer leak | Stains that grow, especially after their shower |
Bathrooms are the most common trouble spot. Our bathroom mold guide explains the difference between grout mildew you can clean and mold that’s coming from behind the tile.
Is it mold, mildew or dirt?
Mildew is flat, powdery and gray or white, sits on the surface of things like grout and wipes off easily. Mold is often fuzzy or slimy, can stain through paint, and returns in the same spot. Dirt and soot don’t grow, spread or smell musty. If you can’t tell, treat it as mold and look for the moisture.
Find the water
Is it a leak or just condensation?
Condensation forms on cold surfaces like windows and outside walls, and gets worse after showers, cooking and on damp marine-layer mornings. A leak shows up in one spot, often after rain or a neighbor’s shower, and the stain grows. The difference matters, because the fix and often who pays for it are different.
| Clue | Points to condensation | Points to a leak |
|---|---|---|
| Where it is | Windows, outside-wall corners, behind furniture | Under fixtures, below a bathroom, near pipes or the roof |
| When it’s wet | Mornings, after showers or cooking | After rain, or when someone uses water upstairs |
| Indoor humidity | Often above 60 percent | Can be normal in the rest of the unit |
A hygrometer is a small, inexpensive humidity meter sold at hardware stores. The EPA recommends keeping indoor humidity below 60 percent, ideally between 30 and 50 percent. Leave one in the problem room for a few days and note readings morning and night. Coastal units in Venice, Santa Monica or San Pedro often run high during May Gray and June Gloom.
Condensation is often improved by running the bathroom fan, cracking a window while cooking, and keeping furniture a few inches off outside walls. But a bathroom with no working fan, single-pane windows that drip, or any plumbing or roof leak is a building problem to report to your landlord. Who is responsible depends on the facts; this isn’t legal advice, so contact Bet Tzedek or a tenant lawyer if there’s a dispute.
Test kits
Do home mold test kits work?
Most store kits can’t tell you much. The common settle-plate kit, a dish you leave open, almost always grows something because mold spores are everywhere, indoors and out. It doesn’t measure how much air was sampled or compare with outdoor air, and it can’t find the source. The EPA notes that if you can see mold, sampling usually isn’t needed.
| Method | What it can tell you | Main limit |
|---|---|---|
| Settle plate (open dish) | That spores landed in the dish | Nearly always positive; no outdoor comparison or air volume |
| Mail-in tape lift or swab | What type of mold a visible spot is | Says nothing about hidden mold or the air |
| Professional spore-trap air samples | Spore counts inside compared with an outdoor control, analyzed by an accredited lab | Costs more; a snapshot of one day |
| Moisture meter and thermal imaging | Where water is inside walls and floors | Finds moisture, not mold itself |
Air sampling earns its cost when you smell mold but can’t see it, when a doctor asks about your home, or when you need lab-backed documentation. Our pages on air quality testing and apartment mold testing for renters explain how it’s done, and the LA inspection cost guide lists typical prices.
Build your record
How do I document mold in my apartment with photos?
Take a wide photo that shows the room, then a close-up with a coin or ruler for scale, and keep the date stamp on. Photograph the same spots every week, plus the leak source and any damaged belongings. Save everything in one folder with a short written log. Good records help with your landlord, a code inspector or a lawyer.
- Shoot before you clean. Photos of the growth as you found it are the evidence. Cleaning first erases it.
- Wide, then close. One photo that shows where in the unit it is, one close-up with something for scale.
- Show the cause. The dripping pipe, the stain from upstairs, the bathroom with no fan, the window that leaks in the rain.
- Repeat weekly. Same angle, same spot. A series that shows growth is more useful than one photo.
- Keep a log. Dates, humidity readings, when you told the landlord, what they said, and any health symptoms your doctor has noted.
Once you have photos, send your landlord written notice. Our landlord mold notice letter is ready to fill in.
Next steps
When should I call someone about apartment mold?
Call your city or county code inspector, for free, if your landlord doesn’t fix visible mold or a leak after written notice. Consider a paid test if the mold is hidden, you have health concerns, or you need documentation. Call right away for active water, like a burst pipe or a ceiling leak during a storm.
Free code inspection
City of LA: LAHD at (866) 557-7368. Unincorporated areas and most other cities: LA County Environmental Health at (888) 700-9995. Read how the free renter inspection works or see who to call in your city.
Paid mold test
Visual inspection with moisture mapping typically runs $250–$500 in LA. With 2–3 air samples and an outdoor control, $400–$800. Your written quote depends on the unit and number of samples.
Emergency water
Tell your landlord or building manager first so they can shut off water. For drying and mold prevention after a leak, we answer 24/7 at (213) 659-0672.
Can I clean small spots myself?
For a small patch on a hard surface, the EPA says you can usually clean it yourself with soap and water, and its guidance uses about 10 square feet as the line for when to bring in help. In a rental, photograph it and tell your landlord first, and don’t paint over it. If it looks black and widespread, read what to do about black mold in your apartment.
Common questions
Apartment mold testing FAQ
How can I tell if my apartment has mold?
Look for spots that come back after cleaning, water stains, bubbling paint or soft drywall, and notice any musty smell. Check under sinks, around windows, on bathroom ceilings and in closets on outside walls.
Are home mold test kits accurate?
Settle-plate kits almost always grow something because mold spores are present everywhere, so a positive result means little. They do not measure air volume, compare with outdoor air or find the source. A mail-in tape lift can identify a visible spot but not hidden mold.
Do I need to test mold I can already see?
Usually not. The EPA notes that when mold is visible, sampling is usually unnecessary to decide it needs to be fixed. Testing helps more when mold is hidden, when a doctor wants data, or when you need documentation for a dispute.
How do I know if it is a leak or condensation?
Condensation appears on cold surfaces like windows and outside walls, mostly in the morning or after showers. A leak stays in one spot, often gets worse after rain or when a neighbor uses water, and leaves a growing stain or soft drywall.
What humidity level causes mold in an apartment?
The EPA recommends keeping indoor humidity below 60 percent, ideally between 30 and 50 percent. Readings that stay above 60 percent make mold growth more likely, especially on cool walls and windows.
How should I photograph mold for my landlord?
Take a wide shot showing the room and a close-up with a coin or ruler for scale, with the date stamp on. Photograph the cause, such as a leaking pipe, and repeat the same shots weekly. Do this before you clean.
Can I get my apartment tested for mold for free?
You can get a free code inspection from LAHD at (866) 557-7368 in the City of Los Angeles or LA County Environmental Health at (888) 700-9995 in unincorporated areas and most other cities. It checks for visible mold and its cause but usually does not include lab testing.
How much does a professional mold test cost in an LA apartment?
Typical Los Angeles ranges are $250 to $500 for a visual inspection with moisture mapping, and $400 to $800 with two to three air samples plus an outdoor control. The written quote depends on the unit and the number of samples.
This page is general information, not legal advice. For questions about your lease or your landlord’s duties, contact Bet Tzedek or a tenant lawyer. Find more help on our renter mold hub for Los Angeles.
Sources
- U.S. EPA, mold and moisture guidance, including the humidity and sampling recommendations: epa.gov/mold
- Centers for Disease Control and Prevention (CDC), mold basics: cdc.gov/mold
- LA County Department of Public Health, Environmental Health: publichealth.lacounty.gov
- Los Angeles Housing Department (LAHD): housing.lacity.gov
Last updated October 2026.
Smell mold but can’t find it?
We find the moisture source, test with an accredited lab, and tell you honestly if the free city inspection is all you need. Call (213) 659-0672, 24/7 across Los Angeles County.