Capers are the small, unopened flower buds of the Capparis spinosa shrub, native to the Mediterranean region. These buds are typically harvested, dried, and then preserved in salt, brine, or vinegar before being used as a pungent condiment. Capers contain proteins that can potentially trigger an immune system reaction in certain individuals. However, immunoglobulin E (IgE)-mediated allergy to capers is considered a very infrequent occurrence.
How Common is a Caper Allergy
IgE-mediated caper allergy is highly uncommon, with only a few documented case reports appearing in medical literature. The vast majority of food allergies are attributed to common allergens such as milk, eggs, peanuts, and tree nuts. The rarity of caper allergy means it is not included on the standard list of priority allergens that must be disclosed on food labels.
Documented cases tend to be concentrated in areas where capers are consumed regularly, such as countries bordering the Mediterranean Sea. Many reported adverse reactions are not caused by a genuine immune response to the caper protein. Instead, individuals may experience non-allergic food sensitivities related to the high concentration of salt or the pickling agents used in preservation. These reactions can sometimes be mistaken for a food allergy, complicating the true prevalence rate.
The Allergic Agents in Caper Buds
Allergic reactions to capers are triggered by specific plant proteins. Although a specific caper allergen has not been universally named, reactions are typically linked to a group of pan-allergens found across the plant kingdom. The primary culprits are often Lipid Transfer Proteins (LTPs) and, to a lesser extent, profilins.
LTPs are a family of highly stable proteins found in the skin, seeds, and pulp of many fruits, vegetables, and nuts. They are particularly resistant to both heat and digestion. This stability allows the protein to survive and enter the bloodstream, increasing the potential for a severe, systemic allergic reaction. Because capers belong to the Capparaceae family, a relative of the Brassicaceae (mustard) family, the allergenic proteins share structural similarities with those found in related plants.
Recognizing Caper Allergy Symptoms and Related Foods
Symptoms of a caper allergy, like other IgE-mediated food allergies, can range from mild to severe and life-threatening. Mild reactions often manifest as Oral Allergy Syndrome (OAS), characterized by itching or tingling in the mouth, lips, or throat immediately after ingestion. Gastrointestinal symptoms, such as nausea, vomiting, or abdominal pain, may also occur.
Skin reactions are common, including the rapid onset of hives (urticaria) or angioedema, which is swelling beneath the skin’s surface. The most serious reaction is anaphylaxis, a rapid, severe response that can impair breathing and cause a sudden drop in blood pressure.
Because the allergic proteins in capers are highly conserved pan-allergens, cross-reactivity is an important factor for those with a confirmed allergy. Individuals allergic to capers may also react to other foods containing similar LTPs or profilins, a phenomenon sometimes called Pollen-Food Allergy Syndrome.
Related foods often include other members of the Brassicaceae family. Cross-reactions are also frequently seen with botanically unrelated foods:
- Mustard seed
- Cabbage
- Broccoli
- Rosaceae fruits like peach and apple
- Tree nuts like hazelnut and walnut
A specialist may use component-resolved diagnostics to precisely identify the protein causing the reaction, which helps to predict the likelihood of these cross-reactions.
Testing and Managing Caper Allergies
Diagnosis of a caper allergy begins with a detailed medical history. The next step typically involves medical testing to confirm the presence of specific IgE antibodies. A skin prick test (SPT) involves placing a small amount of caper extract on the skin and observing for a localized hive-like reaction.
Alternatively, a blood test can measure the level of IgE antibodies. If the results are inconclusive, an allergist may recommend a controlled oral food challenge, which is the most definitive diagnostic tool. Management for a confirmed caper allergy centers on the strict avoidance of capers and any foods prepared with them. For individuals with a history of systemic or severe reactions, emergency preparedness is paramount, requiring carrying and knowing how to use an epinephrine auto-injector immediately if accidental ingestion occurs.