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Column originally published Jan 7, 2003

Mould Can Be A Serious Trigger Of Allergy And Asthma

Question: Our one-year-old son has been sick since September. He was always congested in his nose and in his chest. Sometimes he would cough to the point of vomiting. When he sleeps, we can hear him breathing at the other end of the house. We live in a fairly new home, but we have found some moulds in the bathroom and in our son’s room. Our family doctor prescribed several courses of antibiotics, but he didn’t get better at all. He was admitted to the hospital before Christmas. The paediatrician told us that his breathing problem might be related to the dampness and moulds in our house. Is this really possible?


Your paediatrician is right. It is very likely that your son’s breathing problem is caused by dampness and moulds inside your home. Let me explain to you in more detail here.

Moulds are plants that do not possess chlorophyll, the green pigment that we associate with plants. There are many species of moulds, and they are present all around the earth. Different regions tend to have some unique species, although many are widely distributed in most parts of the world.

Most of the moulds grow outdoors and they are responsible for decomposition of organic matters. Therefore, moulds are nature’s tools to recycle things. Different moulds grow best under somewhat different conditions.

Moulds can also be found indoors, especially when humidity is high. Since houses are built much more air-tight in the last few decades (in order to conserve energy), moulds have become a greater problem in many homes. During fall and winter, doors and windows are naturally closed because of cooler temperature. Humidity tends to build up, especially in the bathroom and kitchen, sometimes even in the basement. If there is any water leakage through the walls, moulds will grow, often behind walls and hard to detect.

Sometimes moulds can be carried indoors, especially if firewood is piled in the basement. Although many people dry the firewood outside, it is never completely dry. Moulds, which are microscopic in nature, are present naturally on firewood. When brought into basement, the cool temperature and dampness provide the ideal environment for moulds to grow and multiply.

We don’t exactly know how moulds affect humans. It is believed that microscopic spores sent out by moulds into the air is the cause of allergic reaction. However, it is also known that many moulds produce volatile chemicals. The role of these chemicals in human disease is not too clear.

The most common mould-induced allergic conditions include allergic rhinitis (allergy in the nose), asthma, and allergic skin rash. Some people would complain of frequent colds when exposed to a mouldy environment. These cold symptoms could be due to allergic rhinitis.

Your son’s problem of chronic congestion in the nose and chest is likely symptoms of allergic rhinitis and asthma. He needs proper treatment for both of these conditions. Antibiotics are not very helpful, although many children with allergic rhinitis can develop sinus infection as a complication.

In addition to medical treatment, you also need to change the indoor environment by reducing humidity and getting rid of the moulds. It is worthwhile to go around the whole house to look for signs of water leakage. This may show up as stains in the wall or ceiling. Sometimes it is necessary to remove the inside walls to properly eradicate the moulds and repair water leaks.

Indoor humidity can be reduced by installing exhaust vents in the kitchen and bathrooms to remove steam while cooking or showering. An air-exchange system can reduce the overall humidity in the house. If you are going to install this system, it is worth your while to get one with a HEPA filter. This specialized filter can remove very small particles including mould spores and dust mites.

I would like to take this opportunity to discuss the use of humidifier in the house. Many parents use them in their children’s room when they are sick, because of the believe that moist air can help with their breathing. Extra humidity can actually cause more harm in the long run.

Most humidifiers put out either cold or hot steam continuously. It is almost impossible to control the amount of steam generated. Excessive humidity can condense on the walls and ceiling, as well as around windows, creating an excellent breeding ground for moulds (and house dust mites). Instead of helping their children getting over their colds faster, parents may unknowingly cause moulds to build up in their rooms, which can cause long-term health hazard for their children.

The ideal humidity in the house is 35-45%. Parents can measure the indoor humidity by purchasing a hygrometer from hardware stores. When humidity is too high, moulds and dust mites will grow.

Many parents are concerned that the house is too dry in winter time. It is very true that when we heat up the air to keep the house warm, the humidity of the air will drop. When humidity is too low, it dries up the nose and throat, sometimes even cause nosebleeds in small children.

However, the best solution is to lower the thermostat instead of using a humidifier. When we lower the temperature, air is not heated as much, humidity in the air would be higher.

I have often seen children coming to my office in the middle of winter, wearing only a short-sleeve T-shirt underneath a big winter jacket. T-shirts are all they wear at home. As a result, parents often crank up the heat to keep the house warm, thereby lowering the indoor humidity.

My recommendation is to wear long-sleeve shirts and sweaters indoors, and keep the temperature relatively low (around 20 degrees C.) in the house. In this way, the house is cool and not too dry, and there is no need to use a humidifier.

For those who rely on wood as the main source of heat, my recommendation is to stack the wood outside, either in an outdoor shack, or next to the house, and just bring in enough wood for one or two days. In this way, we can reduce the amount of moulds that is brought into the house. Unfortunately this will not eliminate the problem of smoke coming out of the wood stove or wood furnace. It is also very difficult to control the indoor temperature when we use wood stove.

Another benefit of turning down the thermostat is reducing the use of fuel, whether it is natural gas, propane, or heating oil. These are all hydrocarbons, and they produce carbon dioxide that causes global warming. By reducing their consumption, we will help Canada to meet the Kyoto requirements.

I hope I have given you an explanation about the connection between the moulds in your home and your son’s illness. Hopefully you are able to remedy the problem in the near future.