Molds are ubiquitous, and mold spores are a common component of household and workplace dust. In large amounts they can be a health hazard to humans, potentially causing allergic reactions and respiratory problems.
Some molds produce mycotoxins that can pose serious health risks to humans and animals. "Toxic mold" refers to molds which produce mycotoxins, such as Stachybotrys chartarum. Exposure to high levels of mycotoxins can lead to neurological problems and death. Prolonged exposure (for example, daily exposure) can be particularly harmful.
Symptoms of mold exposure may include:
- Nasal and sinus congestion; runny nose
- Eye irritation; itchy, red, watery eyes
- Respiratory problems, such as wheezing and difficulty breathing, chest tightness
- Throat irritation
- Skin irritation, such as a rash
- Persistent sneezing
Infants may develop respiratory symptoms as a result of exposure to Penicillium, a fungal genus. Signs of mold-related respiratory problems in an infant include a persistent cough or wheeze. Increased exposure increases the probability of developing respiratory symptoms during the first year of life. Studies have indicated a correlation between the probability of developing asthma and exposure to Penicillium.
Mold exposure has a variety of health effects, and sensitivity to mold varies. Exposure to mold may cause throat irritation, nasal stuffiness, eye irritation, cough and wheezing and skin irritation in some cases. Exposure to mold may heighten sensitivity, depending on the time and nature of exposure. People with chronic lung diseases are at higher risk for mold allergies, and will experience more severe reactions when exposed to mold. Damp indoor environments correlate with upper-respiratory-tract symptoms, such as coughing and wheezing in people with asthma.
Causes and growing conditions
Molds are found everywhere, and can grow on almost any substance when moisture is present. They reproduce by spores, which are carried by air currents. When spores land on a moist surface suitable for life, they begin to grow. Mold is normally found indoors at levels which do not affect most healthy individuals.
Because common building materials are capable of sustaining mold growth and mold spores are ubiquitous, mold growth in an indoor environment is typically related to water or moisture and may be caused by incomplete drying of flooring materials (such as concrete). Flooding, leaky roofs, building-maintenance or indoor-plumbing problems can lead to interior mold growth. Water vapor commonly condenses on surfaces cooler than the moisture-laden air, enabling mold to flourish. This moisture vapor passes through walls and ceilings, typically condensing during the winter in climates with a long heating season. Floors over crawl spaces and basements, without vapor barriers or with dirt floors, are mold-prone. The "doormat test" detects moisture from concrete slabs without a sub-slab vapor barrier.
Significant mold growth requires moisture and food sources and a substrate capable of sustaining growth. Common building materials, such as plywood, drywall, furring strips, carpets, and carpet padding provide food for mold. In carpet, invisible dust and cellulose are food sources. After water damage to a building, mold grows in walls and then becomes dormant until subsequent high humidity; suitable conditions reactivate mold. Mycotoxin levels are higher in buildings which have had a water incident.