Allergy shots or allergen immunotherapy refer to treatment with frequent injections over time to reduce or stop allergic reactions. An eye allergy (allergic conjunctivitis) is an adverse immune reaction triggered by contact with an irritating substance (allergen). Allergens include dust, smoke, pollen, feathers, dust mites, or animal hair. Usually, the body's immune system is built to fight against viruses and bacteria. However, in people with allergies, the body's immune system mistakes an allergen for something dangerous, triggering the release of chemicals to fight what may otherwise be harmless. The result is irritating symptoms like redness, itchiness, and swollen eyelids in the morning. Sometimes eye allergies may lead to asthma, eczema, sneezing, congestion, and runny nose. 

Allergy shots are considered in severe cases of allergy where over the counter medications have failed. They are also a good treatment option for those who are allergic to insect stings and want to reduce the use of allergy drugs in the long-term. In each shot is a small amount of the allergens that trigger the specific person’s allergic reaction. Those with seasonal allergic reactions such as hay fever and asthma may be allergic to pollen, while those with indoor allergies may be allergic to dust mites, dander from pets, or cockroaches. All these will benefit from allergy shots. 

The allergens in the shot can stimulate the immune system but are not sufficient enough to lead to an adverse allergic reaction. The more shots (with an incremental dose) one receives over time, the more the body gets desensitized to tolerate the allergies. Over time, the symptoms will disappear. The shots are usually administered over five years, with the most noticeable improvement in the symptoms occurring in the third year. Some people have no significant allergic reaction after successful treatment even years after stopping the allergy shots, while others will require continuous shots to control the allergic response.

Administration & Dosage

Certain tests need to be done to determine the specific allergens one reacts to and the reaction caused by the allergy. The skin test involves scratching the suspected allergen into the affected person’s skin, followed by observation of the area for approximately 15 minutes. If the area swells and becomes red, the person is allergic to that substance. 

Before the administration of the shot, the physician must establish the health of an individual. The doctor needs to know if the patient has asthma. The physician will want to know about any medications or supplements the patient may be taking that may interfere with treatment. The patient should avoid strenuous activity at least two hours before the shot and for several hours after the shot. Exercise tends to boost blood low to the tissues causing the allergies to spread faster throughout the body. 

The shots are administered in two phases:

Build-up phase
The patient receives injections in the upper arm once to thrice a week. Each next dose contains increasing amounts of the allergen. This phase lasts from three to six months, depending on one's reaction. 

Maintenance phase
In this phase, there are more prolonged periods between the shots, which range from 2-4 weeks. Generally, shots are administered once a month. This phase only starts after an effective dose has been attained in the build-up phase and depends on the patient’s allergen sensitivity level and response to the first phase. This phase lasts from three to five years. 

Some cases require ‘rush immunotherapy.’ This refers to the patient receiving increasing doses of the injection every time they visit the doctor. Although it shortens the duration of treatment, it increases the risk of a severe reaction.

The patient needs to stay back in the physician’s office for approximately 30 minutes in case of side effects or a reaction. 

Potential Side Effects & Interactions

Reactions to allergy shots do occur in some people. Local reactions are more common and include irritation, swelling, or redness at the site of the injection. However, these typical reactions disappear in about 8 hours. Systemic reactions are not so common but are more serious and include sneezing, hives, or nasal congestion. Other more severe systemic reactions include tightness in the chest, wheezing, and swelling in the throat. A severe life-threatening reaction is known as anaphylaxis, where a patient develops low blood pressure and breathing complications. This rare reaction can start half an hour after the injection but can also begin later.

These reactions can be minimized by getting allergy shots weekly or monthly and right on schedule without missing any dose. Antihistamines taken before the shots can help reduce the risk of a reaction. Certain medications for lung and heart disease may interfere with treatment and should be declared upfront.

Symptoms of Overdose

Though rare, incorrect doses have been shown to cause mild to severe reactions as well as fatalities.