Most people don't have much trouble with allergy shots. But they contain the substances that cause your allergies — so reactions are possible, and can include:

  • Local reactions, which can involve redness, swelling or irritation at the injection site. These common reactions typically begin within a few hours of the injection and clear up soon after.
  • Systemic reactions, which are less common — but potentially more serious. You may develop sneezing, nasal congestion or hives. More-severe reactions may include throat swelling, wheezing or chest tightness.
  • Anaphylaxis is a rare life-threatening reaction to allergy shots. It can cause low blood pressure and trouble breathing. Anaphylaxis often begins within 30 minutes of the injection, but sometimes starts later than that.

If you get weekly or monthly shots on a regular schedule without missing doses, you're less likely to have a serious reaction.

Taking an antihistamine medication before getting your allergy shot can reduce the risk of a severe reaction. Check with your doctor to see if this is recommended for you.

The possibility of a severe reaction is scary — but you won't be on your own. You'll be observed in the doctor's office for 30 minutes after each shot, when the most serious reactions usually occur. If you have a severe reaction after you leave, return to your doctor's office or go to the nearest emergency room.

Feb. 22, 2012