An allergic reaction is an overreaction of the immune system to a substance called an allergen. Allergens such as pollen, mold, chemicals, plants, and medications do not cause problems in most people. However, the immune system in some people reacts to allergens by sending out chemicals and cells that make body tissues inflamed. Different tissues can be affected, such as the skin, eyes, nose, airways, and lungs.

An allergic reaction can range from mild and annoying to severe and life-threatening.

• Allergic reactions can be local and produce swelling, itching, or hives in the area of contact with the allergen.
  • Hives can be minor, or they can be the first sign of a life-threatening allergic reaction (anaphylaxis).
  • Local reactions can usually be handled at home and are not life-threatening.
• Other allergic reactions may affect the whole body, causing itching, swelling, and even difficulty breathing. Many allergic reactions after a body piercing are allergic reactions to the metal in the jewelry and can be prevented.

Allergic reactions do not always occur the first time a person is exposed to an allergen. Allergic reactions can become worse with each exposure. The first reaction may be mild. The next may be moderate or life-threatening.

Sometimes a local reaction is the start of a more serious full-body reaction to the allergen. A more serious reaction may include throat swelling, difficulty breathing, wheezing, or a generalized rash or hives. Blood vessels may be involved and can cause a circulatory collapse (anaphylaxis). Symptoms may start slowly or occur all at once. Breathing difficulty that comes on suddenly usually is a serious problem.