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
In the warmest areas of the United States, however, molds thrive all year and
can cause year-round (perennial) allergic problems. In addition, molds growing
indoors can cause perennial allergic rhinitis 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, mushrooms, 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
molds 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 by
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
In general, Alternaria and Cladosporium (Hormodendrum) are the molds most
commonly found both indoors and outdoors throughout the United States.
Aspergillus, Penicillium, Helminthosporium, Epicoccum, Fusarium, Mucor,
Rhizopus, and Aureobasidium (Pullularia) are also common.
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?
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
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.
Fungus has been noted to cause sinus disease as well; this is termed Allergic
Fungal Rhinosinusitis. Allergic patients can develop an allergy to a
fungus that happens to deposit within a sinus cavity. These patients
always present with nasal polyps, and sinus symptoms that do not clear with
medical, i.e., antibiotic, therapy. Surgery and allergic desentization are
usually both required to satisfactorily control the disease.