mold
Meaning of mold: Whether mold matters to health depends far more on the species and on the person exposed than on the presence of mold itself.
Definition of mold
Mold is a common name for fungi that grow as multicellular networks of branching filaments rather than as single cells. Molds release spores into the air, which is how they spread and take hold wherever conditions suit them, including damp indoor surfaces and decaying organic material. Spores are present in ordinary air almost everywhere.
What kind of organism is a mold?
Molds belong to the kingdom of fungi, which is separate from both plants and animals. They do not photosynthesize. Instead they release enzymes into the material they sit on and absorb what those enzymes break down. A mold grows as a mat of fine threads called hyphae, which together make up a mycelium, and it is this filamentous habit that separates molds from yeasts, the single-celled fungi. The fuzzy or powdery surface seen on old bread or a damp wall is the reproductive layer, busy making spores. Spores are light, tough and produced in enormous numbers, which is why they travel on air currents and survive conditions that would kill the growing mold itself.
What can exposure actually do?
| Effect | Mechanism | Who it affects |
|---|---|---|
| Nothing | Spores are inhaled and cleared | Most people, most of the time |
| Allergy | An allergic response to proteins in the spores | People sensitized to that particular mold |
| Irritation | Direct irritation of airways and eyes | Anyone, where spore levels are high |
| Infection | The mold itself grows within tissue | Mainly people with severely weakened immune defenses |
Allergic symptoms are those of any airborne allergy: sneezing, a blocked or running nose, itchy eyes, and worsening of asthma in people who have it. Infection is a different matter entirely, because it requires that the immune system be unable to stop the organism growing. Invasive mold infection is therefore concentrated among people receiving intensive chemotherapy, transplant recipients, and others whose defenses are markedly reduced. Some molds also produce mycotoxins, chemical byproducts studied largely in relation to contaminated food and animal feed.
What does finding mold mean?
On its own, very little, because mold spores are a normal component of both outdoor and indoor air. What changes the picture is visible growth indoors, since that indicates persistent moisture; mold cannot establish itself on a dry surface. Identifying the species matters more than counting spores, as species differ widely in how allergenic they are and in whether they can infect tissue at all. The health of the person exposed matters just as much, since the same growth in the same room raises an entirely different question for someone with asthma or suppressed immunity than for someone with neither.
Used in a sentence
The patient's chronic sinus symptoms prompted testing for a possible mold allergy.
Good to know
Mold exposure causes an allergic reaction in some people and, far less commonly, an invasive infection in people with significantly weakened immune systems, two distinct effects that call for different evaluation.