Mold Characteristics & Health Effects

Mold fragments and spores (the microscopic reproductive units of molds) are fungi that are present everywhere on earth, in air and dust, both indoors and outdoors. No one knows how many species of fungi exist, but estimates range from tens of thousands to perhaps three hundred thousand or more. Molds grow best in warm, damp, and humid conditions, and spread and reproduce by making spores. Mold spores can survive harsh environmental conditions, such as dry conditions, that do not support normal mold growth. 

Mold grows in buildings if the indoor air is very damp or if there have been water leaks. You may suspect that mold is present if you see visible growth or if you smell moldy odors. Exposure to mold may affect your health, the severity depends on several factors, including:

• The amount and type of mold present.
• How close the person is to the area of mold growth.
• How much time he or she spends in the building.
• The person's susceptibility to mold's effects.

Molds usually cause adverse health effects when they are inhaled in large numbers. The number of mold fragments or spores needed to cause health problems is unknown and varies from person to person. Some people report no problems even in very moldy environments; persons who are allergic to molds may respond to just a very few spores. Besides inhalation, people can become exposed to mold through skin contact and food. Some molds also produce compounds called toxins or mycotoxins. In high concentrations, these compounds may cause symptoms even in individuals who have no allergies. The following symptoms may be caused by mold allergies:

• Nasal or sinus congestion
• Sensitivity to light
• Sneezing
• Sore throat
• Cough
• Skin irritation (rash or itching)
• Shortness of breath
• Headache
• Watery, reddened, or burning eyes
• Fatigue
• All of the reported symptoms are non-specific and can be caused by many other health conditions. Therefore, it is very difficult for physicians and environmentalists to determine whether specific symptoms are tied to mold exposure. Symptoms are similar to many other illnesses, including colds, flu, and hay fever from pollen. Other similar triggers could be dust, fibers from clothing or carpeting, animal dander, pollen, air pollutants, perfumes and cleaning compounds. 

People that are most at risk from mold exposure are infants, toddlers, children, the elderly, those with compromised immune systems, and people with existing respiratory conditions such as allergies or asthma tend to have a higher risk for health problems from elevated levels of mold spores. Damp buildings and mold growth are recognized triggers of asthma attacks. 

Allergy tests can identify allergies to fewer than ten of the hundreds of molds that can grow indoors. Therefore, students or staff may have mold allergies that a doctor cannot accurately diagnose with an allergy test. There is no blood, urine, or other medical tests that can determine whether someone has been exposed to a mold toxin. 

Generally, it is not necessary to identify the species of mold growing in a building or residence, and CDC does not recommend routine sampling for molds. Current evidence indicates that allergies are the type of diseases most often associated with molds. Since the susceptibility of individuals can vary greatly either because of the amount or type of mold, sampling and culturing are not reliable in determining your health risk. If you are susceptible to mold and mold is seen or smelled, there is a potential health risk; therefore, no matter what type of mold is present, you should arrange for its removal. Furthermore, reliable sampling for mold can be expensive, and standards for judging what is and what is not an acceptable or tolerable quantity of mold have not been established.

For more information about mold, visit:

• CDC – Indoor Environmental Air Quality
• American Industrial Hygiene Association