ALLERGIES - Medicine for Mountaineering and Other Wilderness Activities - page 324

CHAPTER 23
ALLERGIES
James A. Wilkerson, M.D.
Principal Contributor
Whenforeignsubstancesenterthebody,theimmunesystemrespondsbyformingantibodies
that combine withtheforeignmaterials tofacilitate their elimination. Whentheforeignsub-
stances (antigens) are bacteria or viruses, antibodies play a large role in preventing or erad-
icating infection. Other foreign antigens also elicit an antibody response.
Once a person has contacted an antigen, antibodies persist in the blood for years or even
for a lifetime. These persistent antibodies provide permanent immunity following infections
such as measles or mumps. Vaccines are composed of dead or weakened organisms that in-
duce immunity by eliciting an antibody response without producing a full-blown infection.
Some vaccines do not elicit an antibody response as effective as that following an actual in-
fection and must be repeated every few years.
Antibodies are proteins known as immunoglobulins (Ig). Various types of immuno-
globulins are classified as G, M, A, E, and D and are usually abbreviated IgG, IgM, and so
on. Occasionally a person reacts to an antigen by forming an excessive amount of antibody,
particularly IgE, the principal antibody responsible for allergic reactions. Contact with that
antigen—or allergen (an antigen that produces an allergic reaction)—results in a strong IgE
response that releases histamine and related substances to produce an allergic reaction.
The periodic injection of gradually increasing amounts of an allergen can sometimes
overwhelm the antibody response. This process, desensitization, eliminates or greatly re-
duces the allergic reaction. If desensitization is stopped, the original allergic condition usu-
ally returns. Nonetheless, desensitization can be useful in helping to control allergic reac-
tions such as hay fever.
Thesubstancestowhichanindividualmaybecomeallergicareunlimited.Foods,pollens,
animal dander, and dust are the most frequent offenders. Reactions to therapeutic agents are
also common. Insect stings, peanuts, and penicillin are notorious for causing anaphylactic
reactions, an uncommon type of allergic reaction that is explosive in onset and can be lethal
if not effectively treated.
HAY FEVER
Pollens, dust, or other allergens in the air and animal dander are the most common causes of
hay fever (acute nasal allergy). Hay fever is rare in a world of ice and snow, whether at high