Black mold: facts vs fear

What is black mold, exactly?

"Black mold" is a nickname, not a scientific category. Most of the time it refers to Stachybotrys chartarum, which CDC describes as a greenish-black mold. It feeds on materials high in cellulose, such as gypsum board, fiberboard and paper, and it needs constant moisture from leaks, condensation, water infiltration or flooding. That last point is the useful one. Stachybotrys does not show up on a dry wall. If you find it, something has been wet for a while.

Plenty of other molds are dark too. Growth on shower grout, window frames or AC vents can look black and be a different, very common mold. You cannot identify a mold by looking at it, and the color tells you little about how risky it is.

Is black mold more dangerous than other mold?

This is where fear runs ahead of the evidence. CDC's position is that all molds should be treated the same with respect to potential health risks and removal. CDC also notes that a possible link between Stachybotrys and a rare lung bleeding condition in infants has not been proven, and that no test shows a connection between Stachybotrys and particular health symptoms.

What EPA does say about mold in general is plain: mold exposure can irritate the eyes, skin, nose, throat and lungs, and people with asthma or weakened immune systems should stay away from moldy areas. If you or someone in your house has symptoms you are worried about, talk with a doctor or other health professional. A mold company cannot answer medical questions, and a mold test cannot either.

Why does it turn up in Houston homes?

Houston gives water plenty of chances to sit inside walls. The climate is hot and humid for most of the year, the AC runs nearly constantly, and heavy tropical rain falls on flat ground and clay soils that drain slowly. Places where Stachybotrys and other dark molds tend to appear include:

• the paper face of drywall behind a slow plumbing leak or a failed shower pan
• wall cavities and lower drywall after flood water, the pattern seen across the city after Hurricane Harvey
• ceilings under an AC air handler whose drain pan overflowed in the attic
• cardboard boxes and paper stored in a damp garage or closet
• subfloor and joists in older pier-and-beam homes where the crawl space stays damp

In its Harvey response report, the Houston Health Department noted that flooded homes were inspected for dangerous conditions such as mold in walls or floors. Flood-damaged drywall that stayed wet for days is the classic setting for this kind of growth. EPA's post-disaster guidance is blunt on this point: if a flooded home could not be dried within 24 to 48 hours, assume mold is growing, whether or not you can see it yet, and plan the cleanup around that assumption. If that sounds like your house, start with flood mold removal in Houston.

Do I need to test to find out if it is Stachybotrys?

Usually not. CDC says it is not necessary to determine what type of mold is growing in your home, and EPA says that when mold is visible, sampling is generally unnecessary. There are also no EPA or federal limits for mold or mold spores, so a lab report naming the species does not come with a pass or fail line.

Testing has its place. A mold assessment consultant may sample to look for hidden growth when there is a musty odor but nothing visible, or to confirm an area was cleaned well enough after remediation. Our guides on whether mold testing is worth it and inspection versus testing explain when it earns its cost. If a home test kit or a sales pitch focuses on the species, keep in mind that the cleanup is the same either way.

How is black mold removed?

The same way as any other indoor mold. The steps are driven by how much there is and what it is growing on, not by its color:

Moldy drywall is cut out rather than scrubbed, because the growth gets into the paper and gypsum. Hard surfaces can be cleaned. Painting over dark spots does not solve anything; EPA says not to paint or caulk over mold. And none of it lasts unless the moisture is fixed, whether that is a supply line, a roof flashing, a condensate line or poor drainage around the slab.

When you hire help in Texas, the assessment and the removal are done by different companies on the same project; that separation is the law. The remediation company should hold a TDLR mold remediation contractor license, which you can check on TDLR's license search. At the end, a passed clearance from the consultant and a Certificate of Mold Damage Remediation show the work met the plan. For dark growth that needs professional removal, see black mold removal in Houston, or the Sugar Land page if you are in Fort Bend County.

Is it mildew or mold?

Mildew is a loose term for mold growing flat on a surface, often gray or black, in showers and on window sills. It is common in humid Houston bathrooms and is often a cleaning and ventilation problem rather than a remediation job. Growth that keeps returning, sits on drywall, or comes with soft or stained material behind it is a different story. For surface growth, mold and mildew cleanup covers the options.

Common black mold myths

• "If it is black, it is the dangerous kind." Color does not identify the species or the risk. CDC treats all molds the same for removal.
• "You need a lab test before you can do anything." Visible mold is reason enough to fix the moisture and remove it.
• "Bleach and a coat of paint will take care of it." Porous materials often have to go, and paint over mold is something EPA specifically warns against.
• "The city will test my apartment for mold." The Houston Health Department responds to indoor air quality issues in apartments, hotels and motels, but it does not do mold inspection or testing; it refers those questions to TDLR. Renters can read mold in a rental in Houston for the repair request process.

What should I do if I find it?

1. Find and stop the water source, or call the trade that can.
2. Keep people with asthma or weakened immune systems out of the area.
3. Avoid disturbing large patches; do not dry-brush or sand them.
4. Shut off the AC if you suspect mold inside the system.
5. Measure roughly how big the area is and photograph it.
6. For anything beyond a small patch, or growth inside walls, schedule a Houston mold inspection with a mold assessment consultant.

For other early warning signs worth checking around the house, see signs of mold in your house. The full list of services local companies handle is on our services page.