Of all human illnesses, “allergy” stands out as the most popular by the public – being a common conversation topic in any occasion.

Strictly speaking, allergy is an undesirable reaction that is not expected from the interaction between the person’s immune system and a substance that is generally tolerated by the vast majority of people. It is an individual’s own hypersensitivity – i.e., an overreaction by the immune system. Exposure to the offending substance (allergen) can be through ingestion (eating), inhalation (smell), skin contact (touch), or through the skin (insect sting or medication injection).

Not every reaction is allergy!

Over-diagnosis of allergy is common, particularly by those individuals who self-diagnose their symptoms. Frequent colds may be misdiagnosed a respiratory allergy – or the reverse! Chest wheezing in young children may be misdiagnosed as allergic asthma whereas there are many other causes for wheezing that a skillful pediatrician or an allergist can sort out and prescribe the appropriate management. Reactions to foods can be to non-allergic causes, such as acute or chronic gastrointestinal diseases. A common example is intolerance to lactose (the milk sugar), which results from reduction or lack of the specific intestinal enzyme that breaks down lactose, and consequently, fermentation of the sugar in the gut produces gas, stomach ache and loose bowel movements. This is an annoying condition but is not as dangerous as allergy to milk proteins. Similarly, medications have many side effects, many of which are predictable. Actually, side effects of medications are by far much more common than allergic drug reactions, yet it is a common practice by patients to lump all as “allergy.” Again, the allergy specialist can sort out this problem – which often results in a remarkable relief to patients and prescribing physicians.

How allergy develops:

For allergy to develop, the person would inherit the genetic predisposition, through one or both parents. Such a genetic trait is usually a general predisposition and occasionally the same type of manifestation or to the same substance as the parents’. Such a trait remains hidden until the immune system gets exposed to the particular allergen and the balance gets disturbed. The duration and intensity of exposure varies widely from one individual to another. A person may become sensitized during infancy to a food that has been recently introduced whereas another person may start to react to a food that has been eaten with impunity for many years. The underlying process is not well understood; it is very complex and involves many genetic and environmental factors.

What substances cause allergy?

Practically, any substance can cause allergy; proteins are much more likely than carbohydrates, fats or chemicals. Although any food can cause allergy, 80-90 percent of the food reactions are caused by a limited number of foods: cow’s milk, egg, peanut, tree nuts, shellfish, fish, soy and wheat. Peanut stands out as the most implicated, followed by tree nuts, shellfish and fish. Likewise, any drug can cause allergy, including vitamins, hormones and simple analgesics. Antibiotics lead the list, followed by aspirin and similar other nonsteroidal anti-inflammatory medications that are widely sold over the counter and are incorporated in many remedies. Physical agents are intriguing causes of allergy in certain individuals who develop hives from skin scratching, pressure, cold, heat or sunlight. Physical exercise may generate chemicals that mediate allergy, and some patients may react to exercise only when preceded within a couple of hours by food ingestion.

How allergy manifests:

About one-third of the general population experience an acute or a chronic allergy of one sort or another – making allergy the most common group of ailments. In subjects who are already sensitized, reaction occurs within a few minutes to a few hours following exposure to the specific substance. The manifestations may affect the gut, the respiratory system, the skin or multiple organs. [The manifestation] can be simple that resolves spontaneously after avoidance of the causative substance or severe enough to cause shock (anaphylaxis) that can be fatal if not immediately treated. The provoking quantity of the substance can be very small and not noticed by the patient consuming a composite meal. Hidden exposures are much more common than being recognized. Minute traces of food proteins are often incorporated in various medication tablets, syrups or injectables – and may not be declared on the label. In the case of insect sting or bite reactions, local swellings are generally normal and are caused by toxic substances, but remote or generalized reactions can indicate severe allergy.

Management of allergy:

An effective management of allergy is identification and avoidance of the cause(s) if possible. This may be applicable to food or drugs, and to some degree pets or insects, but less so for mold and dust mites, and not possible for pollens. A wide variety of medications are mainly for symptomatic treatment or for long-term control. Patients with a history of severe allergies should wear a Medic-Alert identification and have epinephrine auto-injectors for quick self-administration when needed to treat an acute reaction. Immunotherapy with specific allergy vaccines are very useful in building immunity, particularly against insect sting allergy, pollens, house dust mites and animal dander.

Sami L. Bahna, MD, DrPH, professor of pediatrics & medicine, chief of Allergy & Immunology Section LSU Health Shreveport.