Allergic Reaction Symptoms, Severe (Anaphylaxis)

Symptoms of a severe allergic reaction (anaphylaxis) may include:

• The sudden appearance of raised, red areas (hives) all over the body.
• Rapid swelling of the throat, mouth, or tongue.
• Trouble breathing.
• Passing out (losing consciousness). Or you may feel very lightheaded or suddenly feel weak, confused, or restless.

A severe reaction can be life-threatening. If you have had a bad allergic reaction to a substance before and are exposed to it again, treat any symptoms as an emergency. Even if the symptoms are mild at first, they may quickly become very severe.