What causes mold allergy?

Updated: Dec 02, 2020
  • Author: Shih-Wen Huang, MD; Chief Editor: Harumi Jyonouchi, MD  more...
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All of the clinical disorders related to mold allergy are caused by repeated exposures to molds and the immune responses of susceptible individuals. The relationships between specific molds and particular disorders are discussed in Pathophysiology.

Molds are potential problems in outdoor and indoor environments. Nearly 20 allergenically important molds are related to the household environment. Among them, Alternaria and Hormodendrum species are the most well recognized.

Favorite habitats include damp, dark places (eg, cellars, bathrooms, garages, attics); rotting leaves or vegetation, indoor plants, and organic plant containers (eg, wicker, straw, hemp); old foam-rubber pillows and peeling wallpaper; furniture stuffed with decaying kapok or cotton; rubber gaskets on old refrigerator doors; dishwashers, drainage sinks, and washing machines; and garbage cans. Water-damaged areas, such as leaky roofs, walls with dry rot, and wet carpets, or areas with poor drainage are also prime habitats for mold (see the images below).

Moisture is trapped in the wall behind a vinyl wal Moisture is trapped in the wall behind a vinyl wall covering.
Large amounts of moisture support fungal growth, a Large amounts of moisture support fungal growth, as is the case with this dry wall covering.
Glues can collect mold. Glues can collect mold.
Soapy shower doors collect fungi. Soapy shower doors collect fungi.
Wet drywall collects mold. Wet drywall collects mold.
Wall coverings can pucker because of mold. Wall coverings can pucker because of mold.

Depending on the areas where surveys are conducted, sterile mycelia and the fungi of the genera Cladosporium, Penicillium, Alternaria, Epicoccum, Aspergillus, Pullularia, and Drechslera are most commonly encountered. Studies have also shown that poorly maintained landscaping, high shade levels, and large amounts of organic debris near the home (including ivy, compost, and bark chips) are highly correlated with the accumulation of indoor molds. Also, the development of mold in room-air humidifiers, cold-mist vaporizers, and air-conditioning systems has received much recent attention.

When mold allergens bind to specific IgE on mast cells of susceptible individuals, mast-cell activation causes an immediate reaction, leading to the early release of histamine. As in the case of other airborne allergens, a delayed allergic reaction is expected to follow, with infiltration of various inflammatory cells that serve to magnify the inflammatory process, which may last for days. Immediate and late mucosal inflammatory processes lead to the development of the signs and symptoms of allergy (see Pathophysiology).

Although genetic factors are known to influence the development of allergies, the exact genetic transmission of each disorder listed in Pathophysiology is currently unknown. Environment plays an important role. In addition to the presence of mold allergens, smoking increases the frequency of allergic rhinitis and asthma. A child with CF is at increased risk for ABPA. Many cases of EAA occur as occupational diseases among individuals working in environments infested with specific molds.

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