Allergic reactions are sensitivities to a specific substance, called an allergen, that is contacted through the skin, inhaled into the lungs, swallowed, or injected.

Allergic reactions are common. In fact, the immune response that causes an allergic reaction is similar to that which causes hayfever. Most reactions happen soon after contact with an allergen.

Many allergic reactions are mild and can be treated at home, while others can be severe and life-threatening. They often occur more frequently in people with a family history of allergies.

Substances that don't bother most of us (such as venom from bee stings and various foods, medications, and pollens) can trigger allergic reactions in some people.

While first-time exposure may only produce a mild reaction, repeated exposures may lead to more serious reactions. Once a person is sensitized (has had a previous sensitivity reaction), even a very limited exposure to a very small amount of allergen can trigger a severe reaction.

Allergic reactions vary. They can be mild or serious. They can be confined to a small area of the body or may affect the entire body.

Most occur within seconds or minutes after exposure to the allergen, but some can occur after several hours, particularly if the allergen causes a reaction after it is partially digested. In very rare cases, reactions develop after 24 hours.

Anaphylaxis is a sudden and severe allergic reaction that occurs within minutes of exposure. Immediate medical attention is needed for this condition. It can get worse very, very fast and lead to death within 15 minutes if treatment is not received. 

Common allergens include:

• Plants
• Pollens
• Animal dander
• Bee stings or stings from other insects
• Insect bites
• Medications
• Foods, especially nuts and shellfish

Common symptoms of mild allergic reactions include:

• Rashes
• Hives (especially over the neck and face)
• Itching
• Nasal congestion
• Watery, red eyes

Symptoms that may indicate a moderate or severe reaction include:

• Swelling of the face, eyes, or tongue
• Difficulty swallowing
• Wheezing
• Fear or feeling of apprehension or anxiety
• Abdominal cramps or abdominal pain
• Nausea and vomiting
• Weakness
• Dizziness or light-headedness
• Chest discomfort or tightness
• Difficulty breathing
• Unconsciousness