Indoor mold (American English) or indoor mould (British English), also referred to as mildew, is a fungal growth that develops on wet materials in interior spaces. Mold is a natural, ubiquitous part of the environment and plays an important part in nature by breaking down dead organic matter such as fallen leaves and dead trees; indoors, mold growth should be avoided as it can affect the structural integrity of buildings and pose potential health risks to susceptible individuals. Mold reproduces by means of tiny spores, which range in size from 1 to 40 microns. The spores are like seeds—but invisible to the naked eye—that float through the air and deposit on surfaces. When the temperature, moisture, and available nutrient conditions are correct, the spores can form into new mold colonies where they are deposited. There are many types of mold, but all require moisture and a food source for growth. Common indoor molds include Aspergillus, Cladosporium, Penicillium, and Stachybotrys chartarum, which contribute to respiratory issues and allergic reactions in sensitive individuals.
Health effects
Indoor mold is generally not regarded as a dominant allergen that affects healthy individuals. However, mold exposure can lead to a range of health effects, with sensitivity differing from person to person. Indeed, the health impact of its exposure depends on factors such as duration, concentration, and type of exposure, which can influence an individual's susceptibility over time. Prolonged exposure and high level of mold exposure can increase the risk of allergic reactions and respiratory diseases, such as asthma, allergic rhinitis, and hypersensitivity pneumonitis. In fact, studies indicate that more than half of adult workers in moldy/humid buildings suffer from nasal or sinus symptoms due to mold exposure. While the risk of infections caused by indoor mold is generally low for healthy individuals, certain populations are more vulnerable. Immunocompromised people and those with chronic lung illnesses, such as obstructive lung disease, are at higher risk for mold allergies and may get serious infections in their lungs when they are exposed to mold. To minimize risks, individuals in these groups should avoid environments prone to mold growth, such as compost piles, cut grass, and wooded areas.
Symptoms Common symptoms of mold exposure may include nasal congestion; sinusitis; rhinorrhea, eye irritation; respiratory difficulties, such as wheezing, chest pain, cough, and persistent sneezing; throat irritation; skin irritation, such as a rash; and headache. Damp indoor environments correlate with upper-respiratory-tract symptoms, such as coughing and wheezing in people with asthma.
Asthma While population-based studies in healthy adults provide limited evidence of a direct causal link between mold exposure and asthma development, research strongly supports the connection between mold exposure in a workplace setting and both the incidence and exacerbation of occupational asthma in adults. Similarly, studies in children have shown that infants in homes with mold have a much greater risk of developing asthma and allergic rhinitis. Infants may develop respiratory symptoms as a result of exposure to Penicillium, a fungal genus. Infants and individuals with asthma who reside in damp indoor environments may experience persistent coughing or wheezing, which could indicate mold-related respiratory issues.
Causes and growing conditions Mold is ubiquitous on Earth and can grow on almost any substance when moisture is present. It reproduces by releasing spores, which are carried by air currents. When these spores land on a moist surface suitable for life, they begin to grow. For indoor mold to thrive, three essential factors are required: nutrients—such as cellulose, commonly found in building materials; moisture—which initiates the decaying process; and time—mold growth typically begins from 24 to 48 hours after the provision of growing conditions.
Common cellulose-based building materials, such as plywood, drywall, furring strips, finish carpentry, cabinetry, wood framing, composite wood flooring, carpets, and carpet padding provide food for mold. In carpet, organic load such as invisible dust and cellulose are food sources. 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 exposure and may be caused by incomplete drying of flooring materials (such as concrete). Flooding, leaky roofs, poor building maintenance, or indoor plumbing problems can lead to interior mold growth. Indeed, after water damage to a building, mold grows in walls and then becomes dormant until subsequent high humidity; suitable conditions reactivate mold. Water vapor often 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. Inorganic materials, such as metal or polished concrete, do not support mold growth, although surface mold growth is still possible. Additionally, insufficient ventilation may accelerate moisture buildup. Visible mold colonies may form where ventilation is poorest and on perimeter walls (because they are nearest the dew point). Mold grows best in warm temperatures, 25 to 30 °C (77 to 86 °F), although growth may occur between 0 and 35 °C (32 and 95 °F).
Removing one of the three requirements for mold growth reduces (or eliminates) new mold growth: moisture, food for the mold spores (for example, dust or dander), and warmth since mold generally does not grow in cold environments.
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