Doctor preparing injection for an allergy shot

How Do Allergy Shots Work?

Allergy shots are a form of immunotherapy. They work by exposing the body in stages to an allergen so that the body ‘learns’ not to react to that trigger. The principle is similar to that of a vaccine, which exposes the body to a small amount of a virus and then allows the body to build its immune response.

How often do you get allergy shots? Allergy shots are administered by a doctor or allergist on a regular basis, typically once or twice a week, during the build-up stage and then less frequently during a maintenance period.

What To Expect During Allergy Shots

Patients can expect to receive shots one to two times a week during the build-up phase. This phase of immunotherapy can take anywhere from three to six months and will vary from patient to patient. Each appointment will be relatively quick, but will involve a period of observation after the shot to ensure there is no reaction.

Shots during the maintenance stage will occur less frequently. The maintenance stage can last anywhere from 3 to 5 years, depending on the patient and condition. Patients can expect to see improvement in symptoms during both stages.


There are several ways in which patients can prepare for their allergy shots. Any preparation, including taking medication, should be done in close consultation with one’s doctor or allergist.


Some doctors may recommend that a patient avoid exercise or exertion in the hours before a shot. This is due to the fact that the increase in blood flow that results from exercise can spread the injectable medication too quickly.


The allergist may also recommend taking an antihistamine in advance of a shot. Patients should also alert their doctor and nurses if they are feeling unwell before a shot, especially if there is a history of asthma.

Side effects of allergy shots

As with any medical intervention, allergy immunotherapy can involve some side effects, which can include:

Local Reactions (Most Common)

Patients may develop redness, irritation or swelling at the site of the shot. These local reactions are common and do not typically last longer than a few hours.

Systemic Reactions (Least Common)

Systemic reactions manifest through sneezing, congestion or even hives. In severe cases, patients may experience swelling in the throat and wheezing.

Anaphylaxis (Extremely Rare)

A patient may go into anaphylactic shock after an allergy shot. This is a life-threatening condition that involves low blood pressure and difficulty breathing.

*Anyone experiencing symptoms of anaphylaxis should seek out medical care immediately.

How To Know It’s Time To Try Allergy Shots

Allergy shots are not right for every patient. Any patient considering allergy shots should consult with their doctor or allergist to discuss their options. How can you know if allergy shots are right for you? Patients are a good fit for allergy shots if they:

  • Have a condition that can be treated with allergy shots
  • Wish to reduce long-term use of allergy medications
  • Have no fear of needles
  • Have no control over exposure to an allergen (i.e. insect sting allergy)
  • Have had little success with controlling symptoms via medications

Frequently Asked Questions

How Long Does It Take for Allergy Shots To Work?

How Effective Are Allergy Shots?

Do Allergy Shots Lower Your Immune System?