Why am I allergic to only certain things?

Some people are allergic to lots of things. Some people are allergic to only one or to very few things. What a person is allergic to is determined by many different factors including the environment, a person’s genes, and the way the immune system works.

The immune system must be able to recognize what to attack, and what not to attack. In a non-allergic person, the immune system can distinguish between foreign cells or substances like bacteria, viruses, or allergens, and cells or substances produced by the body. It does this by using the chemical or molecular structure of substances. This is very important so that harmful ‘non-self’ things are eliminated and helpful ‘self’ things are not. Autoimmune diseases such as lupus or rheumatoid arthritis occur when the immune system malfunctions and attacks normal, ‘self’ cells of the body.

In allergies, each different type of allergen has a unique chemical or molecular structure – that’s why pollen is pollen and mold is mold: they’re chemically different. The immune system’s white blood cells use the ‘blueprint’ of this chemistry to make special proteins called antibodies. These antibodies (called IgE in the case of allergies) are therefore specific to the one type of allergen that they were created to fight against. For a person to become allergic to anything, they must have two exposures to any allergen: the first, or ‘primary exposure’, and the second ‘re-exposure’.

Read a hypothetical story about how allergy happens.

What should I know about the most common allergens?

This information has been approved by David Tinkelman, M.D. (February 2006).