Allergies and Hypersensitivities - Common allergens

The allergens responsible for so many unpleasant and uncomfortable symptoms take a variety of forms too numerous and sometimes too obscure for any book to enumerate. Discussed below are some of the more common types of allergens.

Foods

Foods are among the most common causes of allergic reactions. While nearly any food substance is a potential allergen to certain sensitive individuals, those most frequently implicated are cow's milk, orange juice, and eggs, all considered essential in a child's diet. However, substitute foods are almost always available. Many natural foods contain vitamin C, or ascorbic acid, found in orange juice. Ascorbic acid also is available in vitamin tablets. All of the essential amino acids and other nutrients in cow's milk and eggs also can be obtained from other food sources, although perhaps not as conveniently packaged for immediate use. Other common food offenders are chocolate, pork, seafoods, nuts, and berries. An individual may be allergic to the gluten in wheat, rye, and oats, and products made from those grains.

Inhaled Allergens

Allergens also may affect the respiratory tract, bringing on sneezing, coughing, and breathing impairment. The substances involved can be pollens, dust, smoke, perfumes, and various airborne chemicals.

Mold Spores

A person also can become allergic to a certain mold by inhaling the spores, or reproductive particles, of fungus. In the nose, the mold spores trigger a reaction in cells of the tissues beneath the mucous membranes that line the nasal passages. This in turn leads to the symptoms of allergy. Because they are small, mold spores can evade the natural protective mechanisms of the nose and upper respiratory tract to reach the lungs and bring on an allergic reaction in that site. Usually, this leads to the buildup of mucus, wheezing, and difficulty in breathing associated with asthma.

Less frequently, inhaling mold spores can result in skin lesions similar to those of eczema or chronic hives. In all but the very warmest areas of the United States, molds are seasonal allergens, occurring from spring into late fall. But unlike pollens, molds do not disappear with the killing frosts of autumn. Actually, frost may help increase the activity of molds, which thrive on dying vegetation produced by cold temperatures.

Dust and Animal Hair

House dust and animal hair (especially cat and dog hair) are also responsible for respiratory allergies in many people. Asthma attacks are often triggered by contact with these substances. Symptoms of dust allergy are usually most severe in the spring and fall, and tend to subside in the summer.

Man-Made Allergens

An example of respiratory allergy caused by man-made allergens is the complaint known as “meat wrappers' asthma,” which results from fumes of the price-label adhesive on the poly-vinyl chloride film used to package foods. The fumes are produced when the price label is cut on a hot wire. When the fumes are inhaled, the result is burning eyes, sore throat, wheezing and shortness of breath, upset stomach, and other complaints. Studies show that exposure to the fumes from the heat-activated label adhesive for as little as five minutes could produce airway obstruction in food packagers.

Another source of respiratory allergy is the photochemical smog produced by motor vehicle exhaust in large city areas. The smog is composed of hydrocarbons, oxides of nitrogen, and other chemicals activated by the energy of sunlight. When inhaled in the amounts present along the nation's expressways, the smog has been found to impair the normal function of membranes in the lungs.

Drugs

Medicines and drugs, such as penicillin, or serums used in inoculations, can cause allergic reactions. Estimates of the incidence of allergy among those receiving penicillin range from one to ten percent. The National Institutes of Health has calculated that just three common drugs—penicillin, sulfonamides, and aspirin—account for as much as 90 percent of all allergic drug reactions. The allergic reactions include asthmatic symptoms, skin rash, shock, and other symptoms similar to tissue reactions to other allergens. Medical scientists theorize that chemicals in certain drugs probably combine with protein molecules in the patient's body to form a new substance that is the true allergen. However, it also has been noted that some persons show allergic reactions to placebo drugs, which may contain sugar or inert substances rather than real drugs.

Insect Venom

Insect stings cause serious allergic reactions in about four of every 1,000 persons stung by bees, fire ants, yellow jackets, wasps, or hornets. A single sting to a sensitive person may lead to a serious drop in blood pressure, shock, and possibly death. There are more than 50 reported fatalities a year, and experts suspect that other deaths occur as a result of insect stings but are listed as heart attacks, stroke, or convulsions.

Sensitivity tests of persons who might be acutely allergic to insect stings have been difficult to develop, because allergic individuals reacted in the same way as nonallergic persons to skin tests performed with extracts from insect bodies. More recently, physicians have found that using pure insect venom produces a reaction that determines whether a person is allergic to the sting. Medical scientists also have isolated the major allergen in an insect venom for use in diagnosing and treating patients who are particularly sensitive to stings.