Allergy shots are treatments to stop or lessen allergy symptoms. The shots are given as a series that lasts 3 to 5 years. Allergy shots are a form of treatment called immunotherapy.

Each allergy shot contains a tiny amount of the substance or substances that trigger allergic reactions. These substances are called allergens. Allergy shots have just enough allergens to alert the immune system but not enough to cause allergy symptoms.

Over time, the dose of allergens increases with each shot. The immune system gets used to the allergens and learns not to react to them, so symptoms improve over time.

Allergy shots may be a good treatment choice if:

• Medicines don't control symptoms well.
• Things that cause allergic reactions can't be avoided.
• Allergy medicines interact with other medicines you need to take.
• Allergy medicines cause bothersome side effects.
• Reducing long-term use of allergy medicines is a goal.
• The allergy is to insect stings.

Allergy shots can be used to control symptoms triggered by:

• Seasonal allergies. Hay fever and seasonal allergic asthma may be reactions to pollens released by trees, grasses or weeds.
• Indoor allergens. Indoor symptoms that last all year are often allergic reactions to dust mites, cockroaches, mold or dander from pets.
• Insect stings. Allergic reactions to insect stings can be triggered by bees, wasps, hornets or yellow jackets.

Allergy shots aren't available for food allergies or long-lasting cases of hives, also called urticaria.

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

• Local reactions are swelling or irritation of the skin or changes in skin color where you got the shot. These common reactions typically begin within a few hours of the shot and clear up soon after.
• Systemic reactions are less common but potentially more serious. Reactions may include sneezing, nasal congestion or hives. More-serious reactions may include throat swelling, wheezing or chest tightness.
• Anaphylaxis is a rare life-threatening reaction to an allergen. It can cause low blood pressure and trouble breathing. Anaphylaxis often begins within 30 minutes of a shot, but sometimes starts later than that.

If you skip scheduled doses of allergy shots, you may have to start taking lower doses again to prevent serious reactions.

Taking an antihistamine medicine before getting your allergy shot can reduce the risk of a reaction, particularly a local reaction. Check with your healthcare professional to see if you should take an antihistamine before your shots.

Because of the risk of serious reactions, you're observed for at least 30 minutes after each shot. If you have a serious reaction after you leave, return to your clinic or go to an emergency room. If you were prescribed an emergency epinephrine autoinjector (EpiPen, Auvi-Q, others), use it right away as directed by your healthcare professional.

Before starting allergy shots, your healthcare professional will use a skin test or blood test to make sure your symptoms are caused by an allergy. The tests show which specific allergens cause your symptoms.

During a skin test, a small amount of the suspected allergen is scratched into your skin. Then the area is observed for about 15 minutes. Swelling or a change in skin color indicate an allergy to the substance.

When you go in for allergy shots, let the nurses or doctors know if you are not feeling well in any way. This is especially important if you have asthma. Also let them know if you had any symptoms after a previous allergy shot.

Allergy shots are usually given in the upper arm.

To be effective, allergy shots are given on a schedule that involves two phases:

• The buildup phase generally takes 3 to 6 months. Typically, shots are given 1 to 3 times a week. During the buildup phase, the allergen dose is gradually increased with each shot.
• The maintenance phase generally continues for 3 to 5 years or longer. You'll need maintenance shots about once a month.

In some cases, the buildup phase is done more quickly. A shortened schedule requires several shots of increasing doses during each visit. This can decrease the amount of time you need to reach the maintenance phase and get relief from allergy symptoms. But it also increases your risk of having a serious reaction.

You need to remain in the clinic for 30 minutes after each shot in case you have a reaction.

To reduce the risk of a reaction, don't exercise vigorously for at least a few hours after you get a shot.

Allergy symptoms won't stop overnight. They usually improve during the first year of treatment, but the most noticeable improvement often happens during the second year. By the third year, most people no longer have bad reactions to the allergens.

After a few years of successful treatment, some people don't have allergy problems even after allergy shots are stopped. Other people need ongoing shots to keep symptoms under control.