Under normal circumstances, most mold types and levels are not harmful to healthy individuals. However, when molds grow indoors, their numbers increase to levels that can become harmful. Long-term exposure to mold may cause or worsen conditions such as asthma, hay fever, or other allergies. The most common symptoms of mold exposure are cough, chest or sinus congestion, runny nose, eye irritations, and aggravation of asthma, chronic respiratory or sinus infections. Depending on the exposure level and your sensitivity to the mold, more serious health effects may result.