Allergy shots, also known as allergen immunotherapy, are a long-term treatment designed to help individuals build tolerance to specific substances that trigger their allergic reactions. They involve administering gradually increasing doses of allergens to modify the body’s immune response, aiming to reduce or eliminate allergy symptoms over time.
Allergy Shots and Diarrhea: Is There a Connection?
Gastrointestinal symptoms, including diarrhea, can occur as a side effect of allergy shots, though they are less common than localized injection site reactions. These symptoms are typically part of a broader systemic reaction, meaning the allergic response affects more than just the injection area. While most reactions are mild, systemic reactions can range in severity, with severe instances like anaphylaxis being rare but possible.
Large local reactions and systemic reactions, including gastrointestinal upset, may occur in 1-5% of patients, often during the initial “build-up” phase. These reactions can manifest shortly after the injection, frequently within 30 minutes, which is why patients are typically monitored in the clinic. However, some systemic reactions, including gastrointestinal issues, can also be delayed, appearing several hours or even up to 24 hours or more after the injection.
Potential Reasons for Gastrointestinal Symptoms
Gastrointestinal symptoms from allergy shots often result from a systemic allergic reaction. During such a reaction, the immune system releases chemical mediators like histamine throughout the body. These mediators, involved in allergic responses, can affect multiple organ systems, including the digestive tract.
These mediators can cause various effects in the gastrointestinal system. For example, histamine can cause smooth muscles in the gut to contract, contributing to abdominal pain or cramping. It can also increase fluid secretion into the intestines, resulting in diarrhea. The allergen concentration in the shot and an individual’s sensitivities can influence the likelihood and severity of these reactions.
Managing and Reporting Gastrointestinal Side Effects
Individuals experiencing diarrhea or other gastrointestinal symptoms after an allergy shot should promptly communicate with their healthcare provider. This communication is important for assessing the reaction and adjusting the treatment plan. While mild, isolated gastrointestinal upset might be manageable at home, severe, persistent, or systemic symptoms warrant immediate medical attention.
Other systemic symptoms signaling a need for urgent care include difficulty breathing, hives away from the injection site, swelling in the throat or face, chest tightness, dizziness, or confusion. Healthcare providers may advise patients to monitor symptoms closely and provide details about their onset, duration, and severity.
In some cases, an epinephrine auto-injector might be prescribed for use in severe reactions. Patients are also typically advised to avoid strenuous exercise or hot baths for a few hours after a shot to help minimize the spread of the allergen.