Allergies and Allergic Reactions

Allergic Reactions

Allergies come in different forms and affect people with varying degrees of severity. An allergic reaction, also known as a hypersensitivity reaction, is a reaction caused by the immune system in response to a foreign substance, or allergen.

Cells within the immune system have the job of sampling their environment to determine what belongs what does not. Some of these cells act as garbage disposals. Macrophages and other antigen presenting cells swallow and chew up the foreign substance and present the resulting ("digestion products"), small peptides (antigen) to another cell type (B lymphocyte) that then becomes a plasma cell and makes an antibody to the antigen. The plasma cell begins to make and release a specific antibody (IgE) into the bloodstream. Plasma cells life span is roughly 10-20 days. The memory of the antigen rests in B memory cells that respond rapidly to an additional antigen exposure.

IgE has a great affinity for receptors on cells in the blood (basophils) and tissue (mast cells) that contain histamine, heparin, and other anaphylactic agents. The antibody sits on the surface of those cells waiting to encounter the antigen that inspired its production. When the antigen is encountered, the cells are stimulated to release their inflammatory products and an allergic reaction ensues.

How Do You Get an Allergy?

Allergies and Allergic Reactions

Allergies may develop with first a mild, then an increasing sensitivity over time, or they may come upon you suddenly. For example, you might find that, after your first bee sting, you are severely allergic to bees. Or, you might find that it took years in a pollen-heavy environment (such as a valley in which the main industry is grass-seed farming), to gradually develop a reaction of increasig severity to that pollen.

Childhood allergies to food and drugs are common. For example, common childhood allergies include allergies to cow's milk, wheat, citrus, peanuts, and carrots. Most people outgrow these allergies by the time they reach puberty. In general, a child does not inherit allergies from the parents--therefore, most allergies are established within an individual due to environmental exposure to allergens.

It is a common myth that people do not acquire allergies when older--for example, greater than 50 years of age. However, you can acquire an allergy at any time in your life, regardless of your age, and you can lose an allergy, or become tolerant, just as abruptly and unexpectedly. A 92-year-old woman may suddenly find herself with an allergy to strawberries, while a 24-year-old man may suddenly discover he is no longer allergic to wheat.

Inherited Allergies, or Atopic Disease

Some allergies are the result of inherited sensitivities to a particular allergen. These allergies are called atopic disease, and can include: allergic rhinitis (inflammation of the nasal passages -- also called hay fever or seasonal allergies), allergic asthma, and eczema. Eczema is atopic dermatitis--commonly called dry skin. Eczema is an inflammation of the skin characterized by redness, itching, and oozing lesions that eventually scab over.

Atopic diseases are distinguished by their tendency to produce allergic reactions to normally harmless inhalants and other substances, such as pollens, molds, animal dander, dust mites, and nuts.