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Moulds and fungi

Mould is usually noticeable and can be white, black, yellow, blue or green in colour.

There are many types of fungi and they can be found everywhere in very large numbers - in the soil and the air, in lakes, rivers, and seas, on and within plants and animals, in food and clothing, and in the human body.

Mushrooms are the most commonly known type of fungi. Mould is another type.

Britain is especially prone to indoor mould because it's damp and cold so often, and because a lot of the houses and buildings are old.

The common places for mould to grow in houses are wallpaper, flooring, behind wall tiles and on window frames. Outdoors, mould can grow on rotting logs and fallen leaves, in compost piles and on grasses and grains.

Mould is usually noticeable and can be white, black, yellow, blue or green in colour. It can also have a velvety, fuzzy or rough appearance, and usually has a musty or stale smell.

How do moulds affect asthma?

Fungi, including moulds, release 'seeds' called spores in to the air. Outside they're usually spread by the wind. Spore numbers increase when there's a sudden rise in temperature in a moist environment, such as when central heating is turned on in a damp house, when wet clothes are dried next to a radiator or when the sun comes out after it's been raining on a warm day.

It's the spores that can cause allergic reactions in some people. Mould and fungal spores are often invisible to the naked eye, which means it's hard to avoid them.

Normally, when people breathe in these spores, their immune system helps get rid of them by coughing or sneezing. If you aren't sensitive to mould, you may never even experience a reaction. But for some people with asthma who are sensitive to mould spores, it can act as a trigger, causing asthma symptoms to get worse.

Who is most likely to be affected by mould and fungus?

Around 37 per cent of people with asthma tell us mould and fungi can trigger their asthma If you have cold-like symptoms that don't end when seasons change, you may be allergic to the spores of mould or other fungi. People with asthma who are more likely to have their asthma triggered by fungal and mould spores include:

  • Babies and children
  • Elderly people
  • People with existing skin problems, such as eczema
  • People with a weakened immune system
  • People with severe asthma.

Common moulds

Different types of moulds release their spores at different times of the year. Have a look at the fungal spore page here for more information on fungal spore seasons in the UK.

Alternaria - this is usually found indoors in damp places, such as showers or under leaky sinks. It grows all year round but is most common in July, August and September.

Aspergillus - this is often found indoors growing on dust, powdery food items such as flour, and building materials, such as drywall. It grows throughout the year, with a small peak in August and September and the highest peak in January and February.

Cladosporium - this grows in both cool and warm places and is usually found on fabrics and wood surfaces. It is found in low amounts most of the year, but peaks in July and August.

Didymella - this is also known as "wet weather spores" and is common during mild, humid nights in the summer between the months of June to September. Didymella can be found outdoors and is widespread on grasses and cereals, particularly wheat and barley.

Penicillium - this is present everywhere, particularly in food causing it to spoil (for example vegetables and fruits, giving it a blue fuzzy texture) and other organic, biodegradable substances such as wood, leaves and grass. It is found throughout the year, with a small peak in August and September and the highest peak in January and February.

Toxic black mould or 'black mould' is a name commonly used for Stachybotrys chartarum. It is usually slimy because of a wet layer on the top. It is extremely dangerous to people, particularly people with asthma. If you find what you think might be Stachybotrys the only way you can tell for sure is to have a mould expert look at a sample under a microscope.

How to reduce your risk of moulds affecting you

Because fungal mould spores are around all year, the best thing you can do to reduce your risk of asthma symptoms is to keep your asthma as well managed as possible. You can find useful tips and advice here.

You can also try some of the tips shared below by people with asthma:

  • Keep an eye on the outdoor fungal spore count so you can be extra sure to stay on top of your asthma when levels are high. Have a look at the fungal spore forecast produced by the University of Worcester (remember that this is the national spore count so this may be different to your area).
  • Check for any water leaks under your sinks, fridge, dishwasher and washing machine, as well as around the toilet, bathtub, shower and hot water tank.
  • Keep the garden clear of fallen leaves and other debris.
  • If mould spores are a trigger for you, avoid areas (such as woodlands, parks, gardens or compost) that may contain mould spores.
  • To prevent mould building up indoors, ensure your house is well ventilated by opening windows regularly.
  • When showering or cooking, use your extractor fan and keep doors closed to prevent damp air spreading through the house.
  • Try not to dry clothes indoors, store clothes in damp cupboards or pack clothes too tightly in wardrobes.
  • Remove any mould from your home. If you suspect mould is a trigger for your asthma, don't try to remove the mould by yourself. Ask someone else such as a friend, family member or a professional to remove it for you instead. Remember to keep the room ventilated when the mould is being removed as there may be spores lingering in the air.
  • If you have toxic black mould in your home, never try to remove it yourself. Disturbing toxic black mould can make it release huge amounts of spores and toxins throughout your home, making your asthma symptoms much worse. Call a professional to remove it for you.
  • If you're living in rented or council accommodation and your home is constantly mouldy and damp even after regular cleaning, contact the housing charity Shelter (0808 800 4444 - calls are free from UK landlines and main mobile networks); or speak to your landlord or the housing department at your local authority.

Last reviewed March 2015