Quick answer
Household mold can affect health, but not everyone reacts the same way. The CDC says exposure to damp and moldy environments may cause a variety of health effects, or none at all; for some people it can cause a stuffy nose, sore throat, coughing or wheezing, burning eyes or skin rash. People with asthma or mold allergies may react severely, and people with weakened immune systems or chronic lung disease may get lung infections. The World Health Organization concludes that living in damp or moldy buildings is linked to more respiratory symptoms and asthma. The practical answer is the same for all molds: remove it and fix the moisture. If you have symptoms, talk to a doctor.
This guide is not medical advice. It summarizes what public health agencies say about mold in homes. For questions about your own health or symptoms, talk to your doctor or your state or local health department.
What the CDC says
The CDC’s overview of mold makes three key points:
- Effects vary. Exposure to damp and moldy environments may cause a variety of health effects, or none at all.
- Common symptoms. For some people, mold can cause a stuffy nose, sore throat, coughing or wheezing, burning eyes, or skin rash.
- Higher-risk groups. People with asthma or who are allergic to mold may have severe reactions. Immune-compromised people and people with chronic lung disease may get infections in their lungs from mold.
What the EPA says
The EPA’s mold course explains that molds produce allergens, irritants and, in some cases, potentially toxic substances called mycotoxins. Its main points:
- Allergic reactions to mold are common and can be immediate or delayed, with hay fever-like symptoms such as sneezing, runny nose, red eyes and skin rash.
- Mold doesn’t have to be alive to cause an allergic reaction; dead mold can too.
- Molds can trigger asthma attacks in people with asthma who are allergic to mold, and can irritate eyes, skin, nose, throat and lungs whether or not someone is allergic.
- Less commonly, mold can cause hypersensitivity pneumonitis, and it can cause infections in people with weakened immune systems.
The EPA adds an important caution: the symptoms people report in moldy buildings, such as headaches, difficulty breathing or skin irritation, may also be caused by other exposures or conditions. It’s important not to assume mold is the cause whenever these symptoms occur.
What the World Health Organization says
In 2009, the WHO published guidelines on dampness and mold, based on a two-year review by 36 experts. According to the WHO, occupants of damp or moldy buildings have up to a 75% greater risk of respiratory symptoms and asthma. Exposure to the microbes and chemicals released in damp conditions is associated with the incidence or worsening of respiratory symptoms, allergies, asthma and immunological reactions, and children are particularly susceptible. The WHO recommends preventing or remediating dampness and mold problems to reduce harm to health.
Dampness, not just mold. Health agencies talk about “damp and moldy” environments together. The WHO explains that in damp conditions, hundreds of species of bacteria and fungi grow indoors and emit spores, cell fragments and chemicals into the air, and it describes dampness as a common problem in many European countries. The EPA notes that lower humidity may also discourage pests such as cockroaches and dust mites. So the health goal is to keep homes dry, not only to remove the mold you can see.
What about “black mold” and “toxic mold”?
The EPA notes that the news media sometimes use “toxic mold” and “black mold” to refer to molds that may produce mycotoxins, or specifically to Stachybotrys chartarum. The CDC says that all molds should be treated the same with respect to potential health risks and removal, and that no test exists that proves an association between Stachybotrys chartarum and particular health symptoms. Color doesn’t tell you the species, and the response is the same.
Do you need to test for mold?
Usually not. The CDC does not recommend mold testing, and says that no matter what type of mold is present, you need to remove it. The EPA notes that if mold is visible, sampling is usually unnecessary, and that there are no EPA or other federal limits for mold or mold spores to compare results against. Sampling can be useful in specific cases, such as checking cleanup, and should be done by experienced professionals.
What to do about mold at home
- Fix the moisture. Leaks, condensation and high humidity. The CDC advises keeping humidity as low as you can, no higher than 50%.
- Clean small areas. The EPA says areas smaller than about 10 square feet can usually be handled yourself. The CDC says mold can be removed from hard surfaces with household products, soap and water, or a bleach solution of no more than 1 cup of bleach per gallon of water.
- Protect yourself. The EPA suggests gloves, goggles and an N-95 respirator during cleanup.
- Get help for larger areas, hidden mold or water damage.
- Talk to a doctor if anyone has symptoms, especially people with asthma, allergies, lung disease or a weakened immune system.
Never mix bleach with ammonia or other cleaners. The CDC warns this produces a poisonous gas. People in higher-risk groups may want someone else to do the cleanup.
Worked example: mixing a bleach solution
Assumed situation: you choose to use bleach on a small hard, non-porous surface and need about half a gallon of solution.
- CDC maximum: 1 cup of household laundry bleach per 1 gallon of water.
- For half a gallon of water: no more than ½ cup of bleach.
- Mix with plain water only, open windows, wear gloves and eye protection, and never add ammonia or other cleaners.
Illustrative example. The EPA notes that bleach isn’t recommended as a routine practice and that soap or detergent and water work for most hard surfaces.
Frequently asked questions
Can mold make you sick?
According to the CDC, it can cause symptoms in some people, such as a stuffy nose, coughing, wheezing, eye irritation or skin rash, while others have no effects. Talk to a doctor about any symptoms.
Is a small patch of mold dangerous?
Health agencies don’t give a “safe” size. The EPA’s guidance is practical: clean small areas promptly and fix the moisture; get help for larger areas. People in higher-risk groups should take extra care.
Is dead mold still a problem?
The EPA says dead mold can still cause allergic reactions in some people, so it should be removed, not just killed.
Who should I contact if my landlord won’t fix mold?
The EPA suggests contacting local, state or federal health or housing authorities, or your state health department, if persistent water problems aren’t addressed.
Sources
- CDC. About Mold: health effects, higher-risk groups, testing, cleanup, humidity.
- CDC. Facts About Stachybotrys chartarum.
- U.S. EPA. Mold Course, Chapter 1: health effects, toxic mold terminology.
- U.S. EPA. Mold Course, Chapter 2: humidity, pests and dust mites.
- U.S. EPA. A Brief Guide to Mold, Moisture and Your Home: sampling, cleanup, renters.
- World Health Organization, Regional Office for Europe. WHO publishes first indoor air quality guidelines on dampness and mould (2009) and WHO guidelines for indoor air quality: dampness and mould.
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