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Health Problems Associated with Indoor Moulds

Exposure to indoor mould has been associated with the following health problems:

  • respiratory symptoms such as coughing, wheezing
  • respiratory infections such as aspergilloses
  • allergic diseases, including allergic asthma and bronchitis
  • unspecific symptoms, e.g., eye and skin irritation, fatigue, headache, nausea, and vomiting.

The moulds most frequently encountered in indoor environment are Penicillium, Aspergillus, Chaetomium, Ulocladium, Stachybotrys, Cladosporium, Acremonium, Mucor, Paecilomyces, Alternaria, and Trichoderma. These moulds are all known to cause different types of inhalation allergy. Some moulds such as Chaetomium, Stachybotrys and Ulocladium thrive under very wet conditions. Their presence in indoor environment is an indication of water problem.

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Indoor Mould: Which are the Bread Moulds?

People will normally talk of bread mould. But which mould is the bread. Bread mould could be any of the moulds that commonly occur on bread. Some of the common bread moulds are Rhizopus stolonifer, Chrysonilia sitophila (red bread mould), species of Aspergillus, species of Penicillium, and Monascus ruber. However, any of the indoor moulds can grow on damp bread.

Mould growth (white stuff) on rye bread

Bread moulds can cause significant losses in bakeries and stores. An outbreak of bread contamination by mould would require careful investigation of the whole bread making and storage processes to identify the source of contamination.

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Indoor Moulds: The Penicillium Species

Penicillium species are very common moulds. About 200 species have been described. They are commonly called the blue or green moulds because they produce enormous quantities of greenish, bluish or yellowish spores which give them their characteristic colours. Their spores are found everywhere in the air and soil. They are the most common causes of spoilage of fruits and vegetables. For example, Penicillium italicum and Penicillium digitatum are common causes of rot of citrus fruits, while Penicillium expansum is known to spoil apples. Most species are active producer of toxins.

Mould identified as Penicillium chrysogenumThe most common Penicillium species in indoor environment is Penicillium chrysogenum. It is widespread and has a wide range of habitats. In indoor environment, it is extremely common on damp building materials, walls and wallpaper, floor, carpet mattress and upholstered furniture dust. It produces a number of toxins of moderate toxicity. It is allergenic and can infect immuno-compromised patients.

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Alternaria And Other Mould Spores As Causes Of Allergy

As far back as 1924 Prof Dr Willem Storm van Leeuwen from The Netherlands suggested that inhaled mould spores such as those of Alternaria could cause asthma. The types of moulds widely known to cause respiratory allergy in humans include Aspergillus, Penicillium, Cladosporium and Alternaria. The allergic responses are mainly due to the inhalation of spores rather than mycelial/hyphal fragments. Allergic reactions to each spore type differ between individuals. Mould allergens also vary in the severity of the allergic reactions they induce. More people, for example, are more sensitive to Alternaria than to Cladosporium. Alternaria also produces more severe reactions, while Cladosporium generally only produces a mild reaction. Cladosporium and in particular Cladosporium herbarum, are often the major contributors to outdoor air-spora. Due to their high concentrations they are a major cause of inhalant allergy and allergic asthma in humans. Occupational pulmonary diseases are common in cheese industry (Penicillium roquefortii), breweries (Aspergillus clavatus) and in mushroom farms (Doratomyces sp).

Alternaria is cosmopolitan and ubiquitous in nature. It is currently comprised of about 40-50 species. Alternaria is a well recognized plant disease causing agent. Species of Alternaria are commonly isolated from dead plant materials, soil, food, and indoor air. Alternaria alternata has been isolated from numerous kinds of organic materials in damp situations, including textiles, stored food, canvas, cardboard and paper, electric cables, polyurethane, jet fuel, sewage and effluents. Airborne spores of Altenaria alternata and A. tenuissima are found in very high numbers in the outdoor environment during fall.

Spores of Alternaria alternata as seen under a microscopeAlternaria alternata is a well recognized allergen with airborne spores and mycelial fragments being responsible for the allergic symptoms in individuals with rhinitis or bronchial asthma. Alternaria sensitivity can also lead to severe and potentially fatal asthma. Studies have shown that up to 70 % of mould-allergic patients have skin test reactivity to Alternaria. It has also been shown that prolonged heavy exposure to Alternaria alternata spores and mycelial fragments mimics that of other allergens such as cat dander and dust mites. Since Alternaria is a seasonal mould then this type of allergy is more prevalent in the fall. A. alternata has also been recorded as an opportunistic pathogen causing skin diseases particularly in immunocompromised patients such as the bone marrow transplant patients.

The presence of Alternaria together with other moulds such as Ulocladium spp and Phoma spp, in indoor environment is indicative of humid conditions. Alternaria alternata is not commonly isolated from indoor building materials and in most instances spores found in indoor air environment may have originated from outdoor sources. A closely related mould, Ulocladium chartarum, which is very common in indoor environment is frequently misidentified in labs as Alternaria alternata. U. chartarum is common on wallpaper and drywall, and has been isolated from emulsion paint, polyurethane, plywood and manila fibre.

Should you have a question on Alternaria or any other mould, please send it to My Question.

Which Moulds Grow in Buildings And Why Do They Grow?

The level of moisture (usually referred to as water activity) in building material determines not only whether mould will grow or not but also the types that colonize the material. Damp materials with a water activity value equal to or greater than 0.90 are usually colonized by strains of Aspergillus fumigatus, Trichoderma spp., Exophiala spp., Stachybotrys spp., Phialophora spp., Fusarium spp., Ulocladium spp., and yeasts such as Rhodotorula spp. Materials with a water activity value ranging from 0.90 – 0.85 are colonized by Aspergillus versicolor while those with water activity values of 0.85 or slightly less are colonized by Aspergillus versicolor, Eurotium spp., Wallemia spp., and Penicillium spp., such as Penicillium chrysogenum and Penicillium aurantiogriseum.

Water leakage through roofs, defective plumbing installations and condensation are the main sources for water damage with subsequent mould growth. The building materials most susceptible to mould attacks are water damaged, aged organic cellulose containing materials such as wood, jute, wallpaper, and cardboard. Moulds that are most frequently encountered in buildings are Penicillium (68%), Aspergillus (56%), Chaetomium (22%), Ulocladium (21%), Stachybotrys (19%), Cladosporium (15%), Acremonium (14%), Mucor (14%), Paecilomyces (10%), Alternaria (8%), Verticillium (8%), and Trichoderma (7%). These moulds are all known to cause different types of inhalation allergy.

Do you have a question concerning indoor moulds? Send it to us at My Question.

Salmonella food poisoning and symptoms

Salmonella food poisoning has been a growing concern in recent news. It has frequently lead to recalls of beef, salads and organic products and, even peanut butter products. Salmonella food poisoning occurs when one eats raw or undercooked foods such meat, poultry, eggs or egg products. Properly cooked food can get contaminated with Salmonella if […]

Legionella pneumophila – Guidelines for Laboratory Interpretation

Legionella pneumophila is a Gram negative, aerobic bacteria that is characterized as an opportunistic pathogen. It is the cause of Legionnaires’ Disease, a severe form of pneumonia and, it is the cause of Pontiac fever, a non-pneumonic form of L. pneumophila infection. Legionella spp.’s mode of transmission is through aerosols or aspiration of contaminated water. The Public Health […]

The Indoor Mold Is An Early Warning Device

The mold (or mould, in the Queen’s English) has been the victim of a bad press. Mention the word and it conjures up an image of something rotting or in the process of decomposition. And yet, were it not for the mold that inspired the discovery of penicillin millions of lives would have been lost. […]