Mold Exposure At Home And The Workplace

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Alternaria sp. A cause of allergy

Mold exposure at home and the workplace can cause allergy in susceptible individuals. Mold allergy symptoms may be difficult to isolate from those caused by other allergy triggers (allergens) such as pollen, dust mites, cockroach allergens, animal allergens (hair, dander, saliva) and chemicals.

Pollen is generally an outdoor problem although it could, in summer, infiltrate into the indoor environment from outdoors.  Pollen is produced outdoors by weeds, grasses and trees. The allergens must be inhaled in order to cause respiratory allergy symptoms.

Mold Allergy Symptoms

Mold allergy symptoms

Sneezing due to mold allergy

There are hundreds of types of molds, but not all of them are responsible for causing allergy symptoms. The range of mold allergy symptoms in susceptible individuals may include sneezing, runny nose, mucous production, cough, congestion, sinusitis, earache, headache, wheezing, and asthma.

It is estimated that about 3-4% of the human population and 10% of atopic people get symptoms from exposure to mold spores while the majority of severe asthma sufferers are allergic to them. A number of mold spore types have similar allergens which mean that those who are allergic to molds are likely to be sensitized to multiple types.

Since different molds release their spores at different times of the year, some people can be affected for large parts of the year. It is difficult to say how much mold is too much as human reactions to allergens can vary greatly depending on individual sensitivity. The length of exposure to mold, the amount of allergens, and individual sensitivity determines the severity of the allergy symptoms.

The higher the exposure to mold spores the greater the number of people that would react. The allergic effect of mold spores and pollen does not depend on whether the mold spores or pollen grains are dead or not.

Common Mold Allergy Triggers


Penicillium sp cause allergy

The commmon mold spore types that trigger allergy and asthma in many parts of the world are Alternaria, Cladosporium, Aspergillus, Penicillium and Didymella. Allergic reactions to each spore type differ between individuals and the allergens vary in the severity of the allergic reaction they induce.

For example, it has been observed that more people are allergic to Alternaria than Cladosporium even though the latter is much more common in the air. Alternaria also produces stronger positive reactions while Cladosporium tends to produce a milder allergic reaction.

However Cladosporium, and in particular Cladosporium herbarum, is often the major contributor to air-spora and due to its high concentrations is therefore a major cause of inhalant allergy and allergic asthma in humans.

Didymella exitialis can trigger severe asthma and also cross-reacts with Alternaria. Didymella exitialis is common on cereal crops, particularly wheat and barley so the risk can increase around harvesting of these crops.

How Does One Get Exposed To Mold Spores?


Cladosporium is a cause of allergy

Since mold spores are everywhere exposure occurs all the time whether we’re at home, workplace or outdoors. Mold spores may enter indoors from the outside through open doorways, windows, and heating, ventilation, and air conditioning systems with outdoor air intakes. People can also bring mold spores indoors on their clothing, shoes, bags, and pets.

People are primarily exposed to molds by inhaling airborne spores. They could also be exposed to mold toxins (mycotoxins) by touching mold or eating contaminated food. Because molds are naturally found outdoors and indoors, living in a totally mold-free environment is practically impossible.

In Conclusion

It is generally agreed that mold is a health hazard and exposure can happen at home, in the workplace or outdoors. However, media “hype” about mold often creates unnecessary concern about exposure to mold. At times people may attribute a wide range of symptoms and even serious illnesses to exposure to mold in their home or workplace, even when there is no active indoor mold growth.

It is important that any person experiencing serious symptoms to discuss their concerns with their family doctor as sometimes the symptoms may not be related to mold exposure.

Click the following link to learn more about our mold testing program.

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Dr Jackson Kung'u
Dr. Jackson Kung’u is a Microbiologist who has specialized in the field of mycology (the study of moulds and yeasts). He is a member of the Mycological Society of America. He graduated from the University of Kent at Canterbury, UK, with a Masters degree in Fungal Technology and a PhD in Microbiology. He has published several research papers in international scientific journals. Jackson has analyzed thousands of mould samples from across Canada. He also regularly teaches a course on how to recognize mould, perform effective sampling and interpret laboratory results. Jackson provides how-to advice on mould and bacteria issues. Get more information about indoor mould and bacteria at

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