There are thousands of known species of molds, which include
opportunistic pathogens, saprotrophs, aquatic species, and thermophiles.
Like all fungi, molds derive energy not through photosynthesis but
from the organic matter in which they live. Typically, molds secrete
hydrolytic enzymes, mainly from the hyphal tips. These enzymes degrade
complex biopolymers such as starch, cellulose and lignin into simpler
substances which can be absorbed by the hyphae. In this way, molds play a
major role in causing decomposition of organic material, enabling the
recycling of nutrients throughout ecosystems. Many molds also secrete
mycotoxins which, together with hydrolytic enzymes, inhibit the growth
of competing microorganisms.
Molds are ubiquitous in nature, and mold spores are a common component
of household and workplace dust. However, when mold spores are present
in large quantities, they can present a health hazard to humans,
potentially causing allergic reactions and respiratory problems.
Some molds also produce mycotoxins that can pose serious health risks
to humans and animals. Some studies claim that exposure to high levels
of mycotoxins can lead to neurological problems and in some cases death.
Prolonged exposure, e.g. daily workplace exposure, may be particularly
harmful. Research on the health effects of mold has not been conclusive.
The term toxic mold refers to molds that produce mycotoxins, such as
Stachybotrys chartarum, and not to all molds in general.
Mold in the home can usually be found in damp, dark or steam filled
areas e.g. bathroom or kitchen, over cramped storage areas, recently
flooded areas, basement areas, plumbing spaces, areas with poor
ventilation and outdoors in humid environments. Symptoms caused by mold
allergy are watery, itchy eyes, a chronic cough, headaches or migraines,
difficulty breathing, rashes, tiredness, sinus problems, nasal blockage
and frequent sneezing. In extremely rare cases, over-exposure to mold
may result in bucal mold growth leading to death by asphyxiation.
Many molds can begin growing at 4 °C (39 °F), the temperature within a
typical refrigerator, or less. When conditions do not enable growth,
molds may remain alive in a dormant state depending on the species,
within a large range of temperatures before they die. The many different
mold species vary enormously in their tolerance to temperature and
humidity extremes. Certain molds can survive harsh conditions such as
the snow-covered soils of Antarctica, refrigeration, highly acidic
solvents, and even petroleum products such as jet fuel.
Xerophilic molds use the humidity in the air as their only water
source; other molds need more moisture. Mold has a musty odor.