Onion is a food which may result in allergy symptoms in sensitised individuals.

Onion Allergy Test: Allergen Exposure

Onions were probably among the earliest cultivated vegetables, with references to onion production dating back 3,000 years. They are native to Mediterranean climates, but are in use worldwide.

Most onions are grown only for the mature edible bulbs, but there are some cultivars, the spring or green onions, or scallions, that are eaten immature, along with the leaves.

The bulb can be eaten raw in salads, sandwich fillings, etc, or cooked or preserved in a variety of ways. Fresh, dried, pickled, canned or even frozen, onion is one of the most common flavourings in many cuisines. The leaves, flowers and sprouted seeds are also eaten.

Onion is used as a homeopathic remedy for a variety of conditions. Onion juice rubbed into the skin is said to be a remedy for baldness. The growing plant is said to repel insects and moles and can therefore be rubbed onto the skin.

The plant juice can be used as a rust preventative on metals and as a polish for copper and glass. A yellow-brown dye is obtained from the skins.

Onion Allergy Test: Allergen Description

The following allergens present in onion have been characterised; a lipid transfer protein, a profilin and alliin lyase.

Diallyl disulphide is a major allergen in Garlic and Onion, causing contact dermatitis. Diallyl disulphide penetrates most commercially available glove types, and therefore patients with Onion contact dermatitis may not be protected by most commercially available gloves.

Onion Allergy Test: Potential Cross-Reactivity

An extensive cross-reactivity among the different individual species of the genus could be expected, as well as to a certain degree among members of the family Alliaceae, including onion, leek, garlic, asparagus, and chives, but the level of cross-reactivity varies among individuals.

Onion contains a lipid transfer protein, which may result in cross-reactivity with other lipid transfer protein-containing foods.

Onion contains a profilin, which may result in cross-reactivity with other profilin-containing plants. However, the clinical significance of this has not been established to date.

Garlic alliin lyase showed strong cross-reactivity with alliin lyases from other Allium species, namely leek and onion.

Onion Allergy Test: Clinical Experience

Onion can induce symptoms of food allergy, asthma, rhinoconjunctivitis, and contact dermatitis in sensitised individuals. Onion is one of the most common causes of contact dermatitis of the hands.

Food-dependent exercise-induced anaphylaxis following the ingestion of Onion has been reported.

Onion has also been shown to be a common cause of eosinophilic oesophagitis in adults.

Other reactions

When Onion tissue is damaged, an enzyme reaction releases sulphur-containing volatile compounds causing tearing and rhinorrhea in people who prepare it for eating.

Onions are high in indigestible carbohydrates that may contribute to flatus.

Onions can prevent blood clotting, but can trigger migraine in susceptible people.

The triggering of asthma after eating pickled Onions due to the preservative sulphur dioxide has been reported.

Onions can be a potent and long-lasting refluxogenic agent in heartburn patients.