Mould and health: symptoms, risks and when to worry

How mould affects your health

Mould grows in damp, poorly ventilated places and releases microscopic spores into the air. Most health problems come from breathing in these spores and the fragments of the mould itself, rather than from touching it. For many people the effect is nothing more than a musty smell, but for others it sets off a clear allergic reaction.

The most common symptoms of mould exposure are:

• Sneezing and a runny or blocked nose
• Red, itchy or watery eyes
• A dry cough or a tickly throat
• Wheezing and shortness of breath
• Skin irritation or a rash

These are the same symptoms as hay fever, dust mite allergy and pet allergy, which is exactly why mould is often missed as the cause. A useful test is timing: if your symptoms are noticeably worse in the affected room, or improve when you are away from home for a few days, mould is a strong suspect.

Who is most at risk

Some people are far more sensitive to mould than others. The groups most likely to be affected are:

• Babies and young children — their airways are still developing, and they spend a lot of time indoors. Damp and mouldy housing is linked to more wheezing and chest infections in children.
• People with asthma or COPD — mould is a common trigger that can make symptoms worse and bring on attacks.
• People with allergies or eczema — existing allergies make a reaction to mould spores more likely.
• Older people — respiratory infections from poor indoor air hit harder with age.
• People with a weakened immune system — for example during chemotherapy or after an organ transplant, mould can cause more serious infections.

If you or someone in your household is in one of these groups, dealing with mould promptly matters more. You do not need to panic, but you should not leave it to spread either.

Is black mould more dangerous?

Black mould, often the species Stachybotrys chartarum, has a reputation for being the most harmful type. The colour of the mould does not tell you how dangerous it is. Many different moulds look black, and moulds of every colour can affect your health if you are sensitive to them.

The NHS and other UK health bodies do not treat black mould as automatically toxic. The real message is simpler: any visible mould growth indoors is a sign of a damp problem and should be removed, whatever its colour. Focus your energy on getting rid of the mould and stopping the moisture that feeds it, rather than trying to identify the exact species.

When mould becomes a health problem

Most people living with a small patch of surface mould will not become seriously unwell. It is worth acting before it gets to that point, but the warning signs below are your cue to take mould exposure seriously:

• Symptoms that persist for weeks and do not improve with normal hay fever or cold treatment
• Asthma that is getting worse, or using your reliever inhaler more often than usual
• A child who is wheezing, coughing at night, or getting repeated chest infections
• Breathlessness, a tight chest, or a cough that will not go away
• Mould that keeps returning after cleaning, or spreads to a large area

If any of these apply, remove yourself from the damp environment where you can, treat the mould and moisture, and see a GP if symptoms continue.

When to see a doctor

You do not need to see a doctor for mild symptoms that clear up once the mould is removed. But make an appointment with your GP if you or your child have:

• A cough, wheezing or breathlessness that does not improve
• Asthma symptoms that are getting worse at home
• Repeated chest infections or a rash that will not heal

Tell the doctor that you live with damp or mould, and roughly how long it has been there. It helps them make the right call.

Get urgent medical help if you or a child have severe breathlessness, a fast heartbeat, or a baby or child who is struggling to breathe, going blue around the lips, or too breathless to feed or speak. Call 999 or go to A&E. This is unlikely to be caused by mould alone, but it always needs checking quickly.

This page is general information, not medical advice. If you are worried about your health or a child's health, speak to a GP or call NHS 111.

Reducing health risks from mould at home

The only lasting way to protect your health is to remove the mould and fix the moisture that lets it grow. Treating the mould without fixing the damp simply means it comes back. Work through these steps:

1. Find and fix the moisture source. This is usually condensation from cooking, showering and drying clothes indoors, or a leak. Our damp checklist helps you work out which.
2. Clean small patches safely. For areas smaller than about one square metre, clean with a mould remover or warm water and mild detergent. Wear rubber gloves and a mask, and open a window while you work. See the mould removal guide for the full method.
3. Ventilate every day. Open windows for 10 to 15 minutes each morning and use extractor fans in the kitchen and bathroom.
4. Control humidity. Keep indoor humidity below about 60% with a dehumidifier in problem rooms, and dry clothes outside or with a vented dryer.
5. Get help for large or recurring mould. If the mould covers more than about a square metre, is caused by a leak, or keeps coming back, get a professional to treat it. See damp and mould treatment for what to expect.

If you rent your home and the mould is caused by a building defect, your landlord is responsible for fixing it. See our guide on landlord responsibility for damp and mould.

Frequently asked questions

Can mould in your home make you ill?

Yes, for some people. Mould releases microscopic spores into the air, and breathing these in can trigger or worsen allergy symptoms such as sneezing, a runny or blocked nose, red itchy eyes, coughing and wheezing. People with asthma, young children, older people and anyone with a weakened immune system are most likely to be affected.

Is black mould dangerous to your health?

Black mould has the worst reputation, but the colour alone does not tell you how dangerous mould is. Any mould can cause health problems if you are sensitive to it or already have a respiratory condition. The important thing is to remove the mould and fix the moisture that lets it grow, rather than worry about which type it is.

What are the symptoms of mould exposure?

Common symptoms include sneezing, a runny or blocked nose, red itchy or watery eyes, a dry cough, wheezing, shortness of breath and a skin rash. They are the same symptoms as many other allergies, which is why mould exposure is often missed. Symptoms that improve when you are away from the affected room or home can point to mould as the cause.

Can mould cause asthma or make it worse?

Mould does not cause asthma on its own, but it is a common trigger that can make existing asthma worse and bring on attacks. Damp and mouldy housing is linked to more respiratory symptoms and a higher risk of asthma in children. If your asthma symptoms are worse at home, or your child is wheezing more, damp and mould are worth investigating.

When should I see a doctor about mould exposure?

See a GP if you or your child have persistent symptoms such as a cough, wheezing, breathlessness or repeated chest infections that do not improve. Tell the doctor you live with damp or mould. Seek urgent help if you have severe breathlessness, a fast heartbeat, or a child struggling to breathe or going blue around the lips — call 999 or go to A&E.

How do I reduce health risks from mould in my home?

Remove the mould and fix the moisture that lets it grow. Clean small patches with a mould remover or mild detergent and water, wearing gloves and a mask. Then reduce humidity by ventilating daily, using extractor fans, and running a dehumidifier in damp rooms. If the mould covers more than about one square metre, or keeps returning, get professional advice.

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