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Mold Allergy
Along with pollens from trees, grasses, and weeds,
molds are an important cause of seasonal allergic rhinitis. People allergic
to molds may have symptoms from spring to late fall. The mold season
often peaks from July to late summer. Unlike pollens, molds may persist
after the first killing frost. Some can grow at subfreezing temperatures,
but most become dormant. Snow cover lowers the outdoor mold count
dramatically but does not kill molds. After the spring thaw, molds thrive
on the vegetation that has been killed by the winter cold.
In the warmest areas of the United States, however,
mold thrives all year and can cause year-round (perennial) allergic problems.
In addition, molds growing indoors can cause perennial allergic even in
the coldest climates.
What is mold?
There are thousands of types of molds and yeast, the
two groups of plants in the fungus family. Yeasts are single cells that
divide to form clusters. Molds consist of many cells that grow as
branching threads called hyphae. Although both groups can probably cause
allergic reactions, only a small number of molds are widely recognized
offenders.
The seeds or reproductive particles of fungi are
called spores. They differ in size, shape, and color among species. Each
spore that germinates can give rise to new mold growth, which in turn can
produce millions of spores.
What is mold allergy?
When inhaled, microscopic fungal spores or, sometimes,
fragments of fungi may cause allergic rhinitis. Because they are so
small, mold spores may evade the protective mechanisms of the nose and
upper respiratory tract to reach the lungs.
In a small number of people, symptoms of mold allergy
may be brought on or worsened by eating certain foods, such as cheeses,
processed with fungi. Occasionally, mushroom, dried fruits, and foods
containing yeast, soy sauce, or vinegar will produce allergic symptoms.
There is no known relationship, however, between a respiratory allergy to
the mold Penicillium and an allergy to the drug penicillin, made
from the mold.
Where do molds grow?
Molds can be found wherever there is moisture, oxygen,
and a source of the few other chemicals they need. In the fall they grow
on rotting logs and fallen leaves, especially in moist, shady areas. In
gardens, they can be found in compost piles and on certain grasses and
weeds. Some molds attach to grains such as wheat, oats, barley, and corn
making farms, grain bins, and silos likely places to find mold.
Hot spots of mold growth in the home include damp
basements and closets, bathrooms (especially shower stalls), places where
fresh food is stored, refrigerator drip trays, house plants, air
conditioners, humidifiers, garbage pails, mattresses, upholstered
furniture, and old foam rubber pillows.
Bakeries, breweries, barns, dairies, and greenhouses
are favorite places for mold to grow. Loggers, mill workers, carpenters,
furniture repairers, and upholsterers often work in moldy environments.
Which molds are allergenic?
Like pollens, mold spores are important airborne
allergens only if they are abundant, easily carried air currents, and
allergenic in their chemical makeup. Found almost everywhere, mold spores
in some areas are so numerous they often outnumber the pollens in the
air. Fortunately, however, only a few dozen different types are
significant allergens.
Are mold counts helpful?
Similar to pollen counts, mold counts may suggest the
types and relative quantities of fungi present at a certain time and
place. For several reasons, however, these counts probably cannot be used
as a constant guide for daily activities. One reason is that the number
and types of spores actually present in the mold count may have changed
considerably in 24 hours because weather and spore dispersal are directly
related. Many of the common allergenic molds are of the dry spore type—they
release their spores during dry, windy weather. Other fungi need high
humidity, fog, or dew to release their spores. Although rain washes many
larger spores out of the air, it also causes some smaller spores to be
shot into the air.
In addition to the effect of day-to-day weather
changes on mold counts, spore populations may also differ between day and
night. Day favors dispersal by dry spore types and night favors wet spore
types.
Are there other mold-related disorders?
Fungi or microorganisms related to them may cause
other health problems similar to allergic diseases. Some kinds of Aspergillus
may cause several different illnesses, including both infections and
allergy. These fungi may lodge in the airways or a distant part of the
lung and grow until they form a compact sphere known as a “fungus ball.”
In people with lung damage or serious underlying illnesses, Aspergillus
may grasp the opportunity to invade the lungs or the whole body.
In some individuals, exposure to these fungi also can
lead to asthma or to a lung disease resembling severe inflammatory asthma
called allergic bronchopulmonary aspergillosis. This latter condition,
which occurs only in a minority of people with asthma, is characterized
by wheezing, low-grade fever, and coughing up of brown-flecked- masses or
mucus plugs. Skin testing, blood tests, X-rays, and examination of the
sputum for fungi can help establish the diagnosis. Corticosteroid drugs
are usually effective in treating this reaction; immunotherapy (allergy
shots) is not helpful.
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