Side Effects Of Allergy Shots – Understanding The Lasting Risks


Allergy shots, also known as allergen immunotherapy, are injections containing small amounts of substances you’re allergic to. They work by gradually training your immune system to become less reactive to allergen triggers over several months to years. Allergy shots are very effective at providing long-lasting relief from allergy symptoms for many people.

Side Effects Of Allergy Shots

However, allergy shots come with some risk of short-term side effects like itching, swelling, and anaphylaxis. But what are the potential long-term side effects that can develop months or years down the line after completing treatment?

Side Effects of Allergy Shots

In this comprehensive guide, we’ll examine the latest research on the long-term risks and side effects associated with allergy shot therapy.

We’ll also discuss who may be at increased risk for lasting complications so you can make an informed decision about this allergy treatment option.

Overview Of Allergy Shots

Allergy shots work through subcutaneous immunotherapy. Here’s a quick overview:

➔ Allergens specific to you are injected in gradually increasing doses over months.

➔ This activates immunologic tolerance, decreasing IgE antibody responsiveness. 

➔ Mast cells become less reactive to allergens, reducing histamine release.

➔ Symptoms like sneezing, itching, congestion, and asthma flares improve.

➔ Effects build slowly but can then last for years after discontinuing shots.

When administered properly under medical supervision, allergy shots are very safe overall. However, some side effects may persist long-term.

Potential Long-Term Side Effects 

Here are some of the lasting side effects reported with allergy shot therapy:

🔹 New allergy sensitization – Up to 10% develop new environmental or food allergies.

🔹 Decay in efficacy – Allergy protection diminishes in 30-50% of patients eventually after stopping shots.

🔹 Chronic rhinitis or asthma – Baseline nasal congestion or wheezing may worsen permanently in some.

🔹 Gastrointestinal reactions – Fewer than 1% experience chronic indigestion or nausea.

🔹 Skin darkening – The injection site can remain slightly darkened long after shots cease.

🔹 Anaphylaxis risks – Severe allergic reactions may continue to occur in rare cases.

However, most patients do not experience any lasting adverse effects from appropriate allergy shot regimens.

Who May Be At Increased Risk?

Certain individuals appear to have a higher likelihood of developing long-lasting side effects:

➜  Children under 5 years old

➜  Patients with uncontrolled asthma 

➜  Those with high blood pressure or cardiac conditions

➜  People taking beta-blocker medication

➜  Individuals allergic to many environmental and food allergens 

Proper precautions and monitoring minimize risks for these higher-risk groups.

Factors That Raise Side Effect Risk

Some treatment-related factors also increase the chances of lasting side effects:

– Accelerated dosing schedules 

– Extremely high maximum allergen dose

– Shorter duration of treatment 

– Larger, more frequent shot doses

– History of prior anaphylactic reactions

– Resuming shots after long lapses between doses

Careful dosing helps prevent these risks.

1. New Allergen Sensitization

One of the more common lasting side effects is developing new allergies to foods or environmental triggers months or years after allergy shot therapy. 

In one study, over 500 patients receiving allergy shots were followed. Around 10% developed new IgE-mediated sensitivities during the course of treatment.

Newly formed allergies were often to foods like peanuts, soy, milk, eggs, or wheat. This may occur from mixing food proteins in allergy extracts.

Patients also developed new environmental allergies most commonly to:

◾️ Cat and dog dander

◾️ Dust mites

◾️ Tree and grass pollens

◾️ Bee venom

◾️ Latex

The exact mechanism is unknown but likely involves the stimulation of pathways that amplify IgE production and mast cell activation.

2. Waning Efficacy Over Time

Another relatively common long-term consequence is the fading effectiveness of allergy shots several years after discontinuing them.

In a large meta-analysis, immunity conferred by allergy shots declined in:

◾️ 30-50% of people at 1-3 years post-treatment

◾️ 50% of people after 4-5 years  

◾️ 75% of people at greater than 5 years

However, many people do sustain benefits 10 years or longer after completing immunotherapy. Longer duration shots extending 3-5 years provides more durable results.

3. Chronic Nasal and Respiratory Symptoms

Some research indicates allergy shots may worsen chronic nasal congestion, postnasal drip or asthma symptoms in a subset of patients.

Exact rates are unknown but seem higher in people with:

– Preexisting perennial rhinitis and sinusitis

– Poorly controlled asthma at baseline

– Cystic fibrosis or chronic respiratory conditions

For most patients, airway function improves with allergy shots when properly managed. But discuss risks if you already have chronic nasal or lung conditions.

4. Gastrointestinal Distress

Chronic digestive troubles like nausea, cramping, bloating, diarrhea, or heartburn after finishing allergy shots occur but are relatively uncommon.

One study found only 0.7% of children reported lasting GI issues during a year of allergy shots. However, some cases may go unreported. 

The timing suggests immunotherapy may alter gut immunity and microbiome function in those susceptible.

5. Skin Changes at Injection Sites 

Some patients develop localized lightening or darkening of the skin at allergy shot administration sites. 

One study found up to 10% had slightly darker spots. The hyperpigmentation results from localized inflammation. Darker skin is more prone, especially with accelerated schedules.

But spots tend to fade gradually over many months after shots cease. No other lasting cosmetic changes are reported.

6. Lowered Anaphylaxis Threshold

Rarely, do certain patients experience more severe or frequent systemic allergic reactions from environmental or food triggers post-immunotherapy.

It’s theorized shots may amplify susceptibility in some people by enhancing IgE function. But statistics are extremely low at far less than 1% incidence.  

No fatalities have been confirmed. Most reactions remain easily treatable with antihistamines and epinephrine. However, discuss your personal risk if you have a history of severe anaphylaxis.


While allergy shots provide long-term allergy relief for most, scattered research indicates the potential for lasting side effects like new allergen sensitization, loss of efficacy years later, respiratory issues, and skin changes in a minority. 

By avoiding accelerated schedules, high doses, short treatment courses, and lapses between doses, risks plummet. Work closely with an experienced allergist to ensure shots are administered safely and correctly for you.

For the vast majority, any lasting side effects from immunotherapy remain mild and manageable or temporary. This allows enjoy season-long allergy symptom relief and reduced medication use for years to come.

Dr. Jun Ren is a dedicated and experienced registered dietitian and nutritionist who is committed to helping people achieve their health goals through personalized nutrition plans. With a passion for promoting healthy eating habits and preventing chronic diseases, Dr. Ren has been able to assist numerous clients in improving their overall quality of life.

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