Can mold in the house make you sick?

This guide summarises public health guidance. It is not medical advice. If you are unwell, see a doctor or nurse practitioner.

What Health Canada says

Health Canada’s guidance on mold states that people living in homes with mold and damp are more likely to have:

• Eye, nose and throat irritation
• Coughing and phlegm build-up
• Wheezing and shortness of breath
• Worsening of asthma symptoms

It also notes associations between damp, moldy housing and the development of asthma, bronchitis and other respiratory infections, and eczema.

Its recommendation follows from that: control dampness indoors and clean up any visible mold, whatever type it is. Health Canada has not set a “safe” level of indoor mold, because people respond so differently.

Who is most affected

• Infants and children
• Older adults
• People with asthma or allergies
• People with chronic lung conditions
• People with weakened immune systems, for example during cancer treatment or after a transplant

For someone with a severely weakened immune system, some molds can cause serious infections. That is a medical matter, and their care team should be told about mold at home.

How mold affects people

There are three broad ways.

Allergic reactions. The commonest. Spores and fragments act like pollen or dust: sneezing, a runny or blocked nose, itchy eyes, skin irritation, and asthma flare-ups in people who have asthma.

Irritation. Mold growth and damp materials release compounds that can irritate the eyes, nose, throat and airways in anyone, allergic or not. The musty smell is part of this.

Infection. Uncommon, and mainly a risk for people with weakened immune systems.

Symptoms people often ask about

Search engines are full of questions about whether household mold causes headaches, tiredness, skin rashes, sinus infections, stomach problems, memory loss, hair loss and more. An honest summary:

• Respiratory and irritation symptoms have the strongest support: nose, throat, eyes, cough, wheeze and asthma.
• Sinus congestion and skin irritation fit the allergic and irritant pattern and are commonly reported.
• Headaches and tiredness are frequently reported by people in damp, musty homes. They have many possible causes, and public health guidance does not list them as established effects in the way it does respiratory symptoms.
• Memory loss, neurological disease, hair loss, digestive illness and similar claims are not established effects of mold in a home in public health guidance. Much of what circulates online goes well beyond the evidence.

None of this means a symptom is imaginary. It means mold should be considered alongside other causes, by someone who can examine you.

Is black mold worse?

Colour does not tell you the species or the risk, and many molds are black. Health Canada does not sort indoor molds into safe and dangerous kinds. It recommends removing any mold growth. See black mold in the house.

Clues that the house is involved

• Symptoms improve when you are away for a few days and return when you come home
• Several people in the household have similar symptoms
• Symptoms are worse in one room, or in the basement
• They began after a leak, a flood or a move
• They are worse in damp seasons
• There is a musty smell, visible mold, condensation or water staining

How quickly symptoms appear

Allergic and irritant reactions can start within minutes to hours of exposure in someone who is sensitive, and settle when the exposure stops. Others notice a gradual worsening over weeks in a damp home. There is no fixed timetable, and no set amount of mold that makes a person ill.

What to do

1. See a doctor if symptoms are persistent, severe or involve breathing difficulty. Tell them about the mold or dampness. Call 911 for severe trouble breathing.
2. Find and fix the moisture. A leak, condensation, high humidity or a past flood. Mold does not grow on dry materials.
3. Remove the mold. Health Canada describes a small area as three or fewer patches with a total area under one square metre, which a householder can generally clean with soap and water while wearing gloves, safety glasses and a well-fitting N95 respirator. It advises a professional for a patch larger than three square metres, for mold that returns, and for mold hidden in walls or ceilings.
4. Do not have sensitive people do the cleaning. Anyone with asthma, allergies or a weakened immune system should stay out of the area during cleanup.
5. Keep humidity down: between 30 and 50 percent, using exhaust fans and a dehumidifier where needed.

Should the house or the people be tested?

The house. Health Canada does not recommend testing the air for mold. Results vary from hour to hour, and there are no health-based limits to compare them with. If you can see or smell mold, the answer is the same whatever a test says: remove it and fix the moisture.

People. A doctor can test for allergies to molds, which helps explain allergic symptoms. Be cautious about commercial urine or blood “mold toxin” tests marketed directly to the public. They are not part of standard medical practice for assessing household mold exposure.

Cleaning can make symptoms worse, briefly

Disturbing mold releases spores and fragments. People often feel worse during a do-it-yourself cleanup. Wear protection, dampen the area before wiping, bag waste in the room, and ventilate. For larger areas, professional remediation isolates the work area so that the rest of the home is not exposed.

Renters

A landlord in Ontario must keep a rental unit in good repair and fit to live in. Report mold and leaks in writing. If health is affected, a letter from your doctor can support a request for repairs. See mold in a rental in Ontario.

After the mold is gone

Irritation and allergy symptoms usually ease once the source is removed and the home is dry, though the time this takes varies from person to person. If symptoms continue, go back to your doctor. Something else may be responsible.

More: mold removal and remediation.