Symptoms of mold (mildew) exposure vary from individual to individual. Some of the symptoms attributed to mold exposure are highly controversial even among the experts. Generally some molds such as Alternaria and Cladosporium cause allergic reactions (commonly referred to as hay fever) to sensitive individuals. Exposure to opportunistic pathogens such as some species of Aspergillus and Fusarium can lead to infection especially to people with weakened immune system. For example, Aspergillus fumigatus can infect the lungs of immuno-compromised individuals causing a disease condition referred to as aspergillosis.

A small group of molds also produce, at some stage of their growth, toxic byproducts (mycotoxins) which are harmful to human health when inhaled, ingested or come into contact with the skin. Some mycotoxins are recognized carcinogens (i.e., they can trigger cancer).

Allergenic symptoms associated with mold exposure include:

• Allergic asthma and bronchitis;
• Non-inflammatory, unspecific symptoms such as eye and skin irritation, fatigue, headache, nausea, and vomiting.