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by Jackson Kungu

Mould spores are tiny structures produced by moulds for reproduction purposes. They are so small that we can hardly see some of them even when magnified 400 times. One cubic meter of outdoor air may contain as many as 100,000 spores. The volume of air we inspire at rest per minute is estimated at 10 liters. Therefore, in an hour we inhale close to 600,000 spores. The air in working environments including moldy buildings may contain up to 1,000,000,000 spores per cubic meter of air.

In indoor environments moulds grow on moist surfaces such as the drywall, wallpaper, carpet, baseboards and heating, ventilation and air-conditioning systems (HVACs). As these moulds grow, a stage is reached when they produce spores. The spores become airborne after drying out or disturbed.

Why are these spores so dangerous to our health? About 20% of the population is allergic to mould spores. Apart from being allergenic, spores of some mould species such as Stachybotrys contain toxic compounds called mycotoxins. Symptoms associated with mould spores may include allergy, headache and fatigue, running nose, sneezing, coughing, pneumonia and Asthma among others. Young children, the elderly and people undergoing medical treatment are particularly susceptible to mould spores.

How can we control indoor mould spores? It is extremely difficult to get rid of spores completely. We can, however, reduce their numbers by controlling mould growth in our houses or offices. Mould growth is associated with moisture problem as a result of flooding, leaks in roofs or plumbing and condensation in case of poor ventilation or inadequate insulation. The key to controlling mould growth is keeping our houses or offices dry by maintaining low relative humidity (below 70%) thus eliminating or slowing the growth of most mould species. Any water leakage should be repaired immediately and the water dried out within 48 hours. Constant monitoring for mould growth in the kitchen, bathrooms, window frames, carpets and baseboards is recommended. The earlier the mould is discovered the cheaper and easier it is to get rid of the problem.

What should you do if you notice mould growing in your house or office? Do not panic! Seek professional advice. Not all moulds are dangerous to health, but no mould should be allowed to grow in our dwellings. Also the health effects of indoor moulds depend on the amount of mould one has been exposed to, length of time of exposure, the types of moulds present and individual’s resistance. Therefore, presence of mould does not necessarily mean the occupants have been exposed.

Which are the most dangerous moulds? People have come to believe that black moulds are the most dangerous. The truth is, color does not determine whether a mould is of health concern or not. To know whether a mould is dangerous or not requires the mould to be identified by a qualified mycologist.

About the Author

Dr. Jackson Kung’u is a Microbiologist who has specialized in the field of mycology (the study of moulds and yeasts). Dr. Kung’u provides how-to advice and identification services for indoor mould and bacteria to homeowners, environmental consultants, institutions and indoor air quality professionals across Canada. Get more information about indoor mould and bacteria at

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