Chris Miller, PHD
Any foreign substance that enters the body and activates our immune system is called an antigen or immunogen. All microorganisms, cells from other people, and many chemicals that are foreign to the body are immunogens. In most cases, reactions of the immune system to immunogens are helpful. The reactions are directed at destroying the immunogens before they harm the body.
An allergy is a harmful reaction by the body to a foreign substance. An allergy is sometimes called hypersensitivity. It occurs in some people when their immune system reacts in a damaging way to certain foreign substances that enter the body.
Immunogens that cause allergic reactions are called allergens. There are hundreds of allergens that may cause allergic reactions, and it`s estimated that about 15 percent of the population experience some type of allergy.
It`s all in the timing
The two types of allergies are based upon which part of our immune system is involved. One type is the antibody-mediated allergy in which the reaction (symptoms) usually appears fairly soon after exposure to an allergen (minutes to hours). Sometimes, though, the reaction occurs later.
The site of exposure to the allergen and the extent of its spread from that site determines what types of symptoms will occur. If the allergen contacts a small part of the body, a local response called atopy occurs. Examples include circumstances such as when allergens such as pollen contact the eyes and nose (hayfever) or are inhaled (asthma).
If the allergen enters and is spread throughout the body, a more widespread body response called systemic anaphylaxis may occur. Sometimes an allergen, such as penicillin, is injected. Or the reaction may be triggered by a bee sting. Systemic anaphylaxis may involve life-threatening concerns such as difficulty in breathing and vascular collapse.
The second type of allergy is the cell-mediated allergy. Reactions usually are delayed a few days after contact with the allergen.
This type includes contact dermatitis involving allergens from poison ivy, nickel in jewelry, or chemicals in cosmetics. In contact dermatitis, the reactions of blisters, itching, and redness occur on the part of skin actually contacted by the allergen.
Waiting for the shocking dose
Since only a portion of the population develops allergies, those affected must have some unknown special ability to recognize certain immunogens as allergens. Some allergies tend to "run in the family," but this is not always the case.
Before people undergo actual allergic reactions, they must first become sensitized. This involves initial exposure to an allergen, which activates the immune system. This usually occurs without causing any symptoms.
Once sensitized to a specific allergen, subsequent exposure (sometimes called the "shocking dose") to that same allergen can cause a reaction with symptoms.
Unfortunately, people seldom know when they have become sensitized to a specific allergen, and it`s only after the shocking dose that they know they are allergic. In some instances, the initial dose of allergen may be large enough to remain in the body while the immune system is being activated (probably taking a few days). The initial dose could then serve as the shocking dose as well.
It is not known exactly how much allergen is needed to sensitize or to cause a reaction, but in some instances it is quite small and unnoticeable.
The most common inhalant allergens include pollens from many types of plants and flowers, mold, and plant spores. Also included are house/office dust, animal dander, and cereal dust.
Ingestant allergens can cause reactions such as nausea, cramping, diarrhea, oral inflammation, and hives. The most common food allergens are codfish, strawberries, wheat products, oranges, milk, and chocolate. Less common food allergens include peanuts, tomatoes, and the protein albumin in egg-whites.
Injectant allergens include the chemicals injected during insect stings, which cause about 40 deaths a year in the United States. Penicillin, which may be injected or taken orally, is involved in about 300 deaths a year in the United States from systemic anaphylaxis.
Latex allergies, of course, raise questions about safety and protection in dentistry - to both the patient and caregiver. Allergies to latex can result in systemic reactions immediately upon exposure or may involve a contact dermatitis.
More and more latex allergies are being reported among medical and dental patients, and 3 to 17 percent of our health-care workers in the U.S. apparently are sensitized to latex. This increase in latex-sensitivity is likely due to the increased use of latex-containing products in health care, particularly gloves.
Not only do latex gloves contain the offending allergens, but these allergens can become associated with the glove powder (usually cornstarch). Putting on gloves causes the latex glove allergens in the powder to become airborne and spread throughout the office.
Latex allergens surface in items other than gloves, including some rubber dams, prophy cups, orthodontic rings, nitrous oxide nose-pieces, stoppers in anesthetic carpules, bite blocks, retraction bands, mixing bowls, suction adapters, O-rings, stethoscopes, and blood-pressure cuffs - not to mention adhesive products, latex paints, and the backing on some carpeting. Gutta percha, which is closely related to latex, also may cause reactions in a latex-sensitive person.
Protection against allergic reactions to latex means avoiding latex. Approaches to the problem in dentistry include adding questions about latex and other allergies to the medical history. High-risk groups may include health-care workers, those who work in the rubber industry or in plants that use latex in a manufacturing process, those with spina bifida, and those with other allergies. The reduction of latex in the office environment includes using non-latex gloves and other non-latex, patient-care items. In addition, powderless gloves reduce the airborne distribution of glove allergen.
Chris Miller is director of Infection Control Research and Services and professor of oral biology at Indiana University.