Aspirin Allergy vs Aspirin Hypersensitivity

Some people have a true allergy to aspirin, characterized by a specific immune response. Others with allergy-like symptoms have non-allergic aspirin hypersensitivity that does not involve this specific response. As incidental as this may seem, a true allergy can sometimes turn deadly, while a hypersensitive reaction is far less likely to do so.

Some studies suggest that around 1% of the population is either allergic or hypersensitive to aspirin. The number rises to around 3% of people in people with asthma. Having nasal polyps increases the risk even further to around 9%.

This article describes the types of responses referred to as an "aspirin allergy," including their symptoms and how they are diagnosed and treated.

How Aspirin Allergy and Hypersensitivity Differ

A true allergy is one in which exposure to an allergy-causing substance (allergen) stimulates the release of an antibody called immunoglobulin E (IgE) which, in turn, triggers the release of inflammatory chemicals called histamine and bradykinin. These are the two chemicals largely responsible for allergy symptoms.

It is also possible to have an "aspirin allergy" without an IgE response. This reaction, referred to as non-allergic aspirin hypersensitivity, involves a different immune response with the same general outcome—namely, the release of histamine and bradykinin.

Even so, the implications can be very different. This is because a true allergy can sometimes lead to a potentially life-threatening, whole-body allergy known as anaphylaxis. In the absence of IgE, the likelihood of anaphylaxis is far less even if the hypersensitive response is severe.

This is why it may be important to differentiate a true aspirin allergy from a non-allergic aspirin hypersensitivity.

Types and Symptoms of Aspirin Allergies

Healthcare providers will often categorize "aspirin allergies" based on the pattern and location of symptoms. These patterns can help ascertain what type of reaction a person is actually experiencing.

Aspirin hypersensitive reactions are commonly classified as follows:

• Type 1: This is when exposure to an NSAID causes symptoms of asthma (shortness of breath, wheezing, chest tightness) and/or rhinosinusitis (runny nose, congestion, sneezing). This is the most common type and may be an indication of either an allergy or non-allergic hypersensitivity.
• Type 2: This is when an NSAID causes urticaria (hives) and/or angioedema (generalized swelling of tissues) in people with a history of chronic hives or angioedema. This is strongly indicative of a true aspirin allergy and an increased risk of anaphylaxis.
• Type 3: This is when an NSAID causes urticaria and angioedema in people with no history of allergy. This is generally considered a "pseudoallergy" indicative of a non-allergic aspirin hypersensitivity.
  

How Aspirin Allergy Is Diagnosed

The diagnosis of aspirin allergy or hypersensitivity is generally made based on symptoms. Unlike some allergies, there are no skin tests or IgE blood tests that can determine if a person is allergic or hypersensitive to aspirin.

If differentiation is needed (often when it is unclear if aspirin or some other NSAID is the cause), an allergy specialist known as an allergist may conduct an oral challenge. This involves consuming a dose of aspirin to see if you experience a reaction.

An oral challenge is performed under close observation in a hospital or clinic in the event of a severe allergic reaction. If one occurs, the allergist can provide an immediate injection of epinephrine to counter the reaction.

How Is an Aspirin Allergy Treated?

The focus of treatment of an aspirin allergy is to avoid aspirin and any other NSAIDs you may be sensitive to. This includes any product containing aspirin, such as Alka Selzer, Vanquish, Pepto-Bismol, Kaopectate, Maalox, Doan’s, Sine-Off, and Pamprin.

By contrast, acetaminophen (Tylenol) is generally considered safe as it is not an NSAID.

If you've had a severe allergic reaction to aspirin in the past, your allergist may recommend that you carry an epinephrine auto-injector called an EpiPen. This allows you to give yourself an emergency injection at the first signs of anaphylaxis.

Aspirin Desensitization

In certain situations, aspirin desensitization may recommended. This involves exposing you to gradually increasing doses of aspirin under the supervision of an allergist until you are no longer reactive.

This is sometimes recommended for people with severe asthma who require surgery to remove nasal polyps. Doing so may lower your risk of polyp recurrence, particularly if you have a history of AERD/Samter's triad.

Aspirin desensitization should only be done under the direction of a qualified allergist and never on your own at home.

Summary

Some people have a true allergy to aspirin, while others have non-allergic aspirin hypersensitivity. Both can cause the same symptoms, but a true allergy involves an antibody called immunoglobulin E (IgE). The distinction is important because people with a true aspirin allergy are more likely to experience a potentially severe allergy called anaphylaxis.

Aspirin allergy is diagnosed based on the symptoms. The main form of treatment is the avoidance of aspirin or anything that contains aspirin. You may also need to avoid other nonsteroidal anti-inflammatory drugs (NSAIDs).