Millions of people around the world are affected by allergies. The tendency to develop allergies or allergic reactions is genetically inherited. It tends to run in families. If you have a personal or family history of allergies and are exposed to certain things in your environment, called allergens, you may become allergic to some of those things. Examples of common allergies include:
How Allergy Was Discovered
In 1902, two French scientists injected dogs with a small amount of extract from the sea anemone (a flower-like marine animal). Nothing happened. A week later, they repeated the procedure in exactly the same way — and watched, amazed, as the dogs developed severe reactions.
The dogs had somehow become sensitive to the formerly harmless substance, and the researchers had discovered allergy. In people with allergies, the immune system reacts to foreign substances that are otherwise harmless as if they were dangerous. These substances are called allergens. Allergy symptoms are the result of the immune system reacting to an allergen. People who have developed an allergy are described as having become "sensitized" to an allergen.
In the decades since those landmark sea anemone experiments, scientists have come to know a great deal about the mechanisms of allergy.