Mould

Mould

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Mould hyphae on wall surface

	Mould is a type of fungus. Moulds consist of many cells that grow as branching threads called hyphae. It releases airborne spores that cause allergic reactions. Each spore that germinates can give rise to new mould growth, which in turn can produce millions of spores.

	Mould eats paint, wallpaper, cotton, other cellulose materials, dust and food debris. Mould grows rampantly in damp places with poor ventilation, such as:

		Bathroom (especially the shower stalls)
		Kitchen, e.g. refrigerator drip trays, places where fresh food is stored, garbage pails etc.
		Mattress, pillow, stuffed toys, carpet, and fabric sofa / chairs
		Closets / wardrobe, stored clothing
		Air conditioners, humidifiers
		Leaking pipes, damp basements
		Walls, oil paintings, house plants

	Such moisture required for mould growth may come from condensation of water vapour on cold surfaces, such as windows in bathrooms and kitchens and the inside surfaces of external walls. Water may also come through the wall after heavy rain. This is often caused by a leaking gutter or downpipe (downspout).

	Ways to reduce mould:

		Pipes and sinks should be properly maintained to prevent water leakage.
		Ensure all water sources in the kitchen and bathroom are properly covered (e.g. cover the lid of the toilet bowl).
		Empty the drain pans of dishes in the kitchen regularly.
		Keep the sink and bath tub as dry as possible after use.
		Vacuum the ceiling, walls, floor, mattress, fabric sofa, oil paintings and other items at home regularly with an efficient vacuum cleaner that does not disperse dust.
		Use a mattress with cotton surface instead of synthetic fibre. The cotton surface will absorb moisture from the body, so that less moisture will be trapped in the fabric inside the mattress.
		Protect the mattress with a dust-mite proven mattress cover, which can also reduce the amount of mould spores deposited from the air to the inside of the mattress.

Allergens from Mould

When the microscopic fungal spores or fungal fragments of mould are inhaled, allergic rhinitis may be resulted in sensitized people. Because mould spores are so small, they may evade the protective mechanisms of the nose and upper respiratory tract to reach the lungs and bring on asthma symptoms. These include build-up of mucus, wheezing, and difficulty in breathing.

In a small number of people, symptoms of mould allergy may be brought on or worsen by eating certain foods, such as cheese processed with fungi. Occasionally, mushrooms, dried fruits, and foods containing yeast, soy sauce, or vinegar will produce allergic symptoms.

When do moulds release spores

In the warm tropical and sub-tropical areas, moulds thrive all year and can cause year-round (perennial) allergic problems. In addition, moulds growing indoors can cause perennial allergic rhinitis even in the coldest climates.

Many of the common allergenic moulds are of the dry spore type; they release their spores during dry, windy weather. Other moulds need high humidity, fog or dew to release their spores. Day favours dispersal by dry spore types and night favours dispersal by wet spore types. Although rain washes many larger spores out of the air, it also causes some smaller spores to be shot into the air.

Contaminated air-conditioning systems may result in hypersensitivity pneumonitis

Hypersensitivity pneumonitis develops in people who live or work where an air conditioning or humidifying unit is contaminated with mould and emits mould spores. The symptoms may resemble those of a bacterial or viral infection such as the flu. Bouts of chills, fever, weakness, muscle pains, cough, and shortness of breath develop 4 to 8 hours after exposure to the allergens. The symptoms gradually disappear when the source of exposure is removed. If hypersensitivity pneumonitis is allowed to progress, it can lead to serious heart and lung problems.

Hypersensitivity pneumonitis is often associated with specific occupations. For example, farmer's lung disease results from inhaling spores growing in moldy hay and grains. Bakeries, breweries, barns, dairies and greenhouses are favourite places for moulds to grow. Loggers, mill workers, carpenters, furniture repairers and upholsterers often work in moldy environment. (more info)

Problems of air-conditioning in mould control

Theoretically air-conditioning can reduce the amount of mould allergens in the air by filtering them out and reducing humidity. However, air-conditioning systems are often not properly maintained to prevent condensation on the cooling coils from building up, and to remove any stagnant water from the system. These encourage rampant mould growth inside the air-conditioning system. The mould spores will then be dispersed freely in the air by the action of the air-conditioning system itself. This effect has been associated with very high levels of fungal spores within homes and offices.

In addition, most domestic air-conditioning systems, including stand-alone units, simply cool and re-circulate the air within the area they operate. They do not necessarily bring in fresh air from outside. This results in poor indoor air quality.

Regular maintenance of stand-alone units and the ductwork of central systems can prevent a build-up of dust and contamination by mould and bacteria. Running the unit for 30 minutes after turning off the cooling function helps to dry out the system and prevent mould growth.

Common species of moulds

The commonest indoor moulds belong to the species of Aspergillus and Penicillium, which grow well wherever the relative humidity is above 70%. Aspergillus niger is dark brown and is mainly responsible for the typical patches of black on persistently damp walls and skirtings. Penicillium is the mould used in the manufacture of “blue cheese”, and is also commonly found in stored fruits, cheese and bread.

A common form of outdoor mould is dark-coloured microfungi from soil and leafy surfaces. Exposure to dry soil or composting plant materials and activities such as cutting grass, harvesting field crops, or merely walking through vegetation may cause rhinitis in mould-sensitive persons.