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f48 Onion

Whole Allergen
Code f48
LOINC 6193-7
Family Amaryllidaceae
Genus Allium
Species Allium cepa
Route of Exposure Ingestion
Source Material Bulbs
Latin Name Allium cepa
Other Names Garden onion
Categories Food Of Plant Origin, Vegetables

Summary

Onion bulbs are rich in minerals, can be ingested both raw or cooked, and are used frequently as an ingredient in salads and cooked dishes worldwide. Despite their widespread dietary use, only sporadic reports exist of allergic reactions to onion ingestion, with reports of anaphylactic reactions after consumption of cooked onion being especially rare. In sensitized individuals, onion handling can induce rhinoconjunctivitis, asthma and contact dermatitis. 

Allergen

Nature

Onion belongs to the family of Amaryllidaceae that includes leek, garlic, chive and rakkyo. The edible part of the onion plant is the bulb, which is rich in minerals and has a characteristic flavor. Onions are ingested both raw or cooked and are frequently used in salads and cooked dishes worldwide (1, 2). Approximately 743 million tons of onions are grown each year in more than 175 countries (3).

Taxonomy

Taxonomic tree of Onion (4, 5)

Domain

Eukaryota

Kingdom

Plantae

Phylum

Tracheophyta

Subphylum

Spermatophytina

Class

Magnoliopsida

Order

Asparagales

Family

Amaryllidaceae

Genus

Allium L.

Epidemiology

Worldwide distribution 

Onion allergy is rare. One study assessed the prevalence of onion sensitivity and clinical symptoms in 8109 general allergic patients. Approximately 30 % of these patients presented symptoms associated with food intake, whilst food sensitization was observed in approximately 37% of these patients. Subsequently, sensitization to onion was observed in 10 people, approximately 1% (6).

A study involving 108 patients with suspected food allergy from Saudi Arabia evaluated specific IgE levels against garlic and onion. Results showed that 13 (12.0 %) patients had specific IgE to both onion and garlic, and only one patient was mono-sensitized to onion (7).

Route of Exposure

Main 

Ingestion.

Detection

Despite its frequent consumption, allergic reactions due to onion ingestion are sporadic and limited to a small number of cases. Onions can induce both immediate and delayed hypersensitivity reactions. In sensitized individuals, onion handling can induce rhinoconjunctivitis, asthma and contact dermatitis (2).

One case study identified a 35-year-old man who had a severe systemic reaction/anaphylaxis requiring hospital treatment after ingesting cooked onions (2). Anaphylaxis was also  reported in a 44-year-old patient after eating raw or lightly-cooked onions, with symptoms including intense itching, urticaria, confusion, blurred vision, transient loss of consciousness, sweating and tachycardia (8). Another patient, with a history of rhinoconjunctivitis and contact urticaria with mugwort and oral itching with peach skin, reported urticaria and oral itching after ingestion of raw onion (6).

Onions release irritating substances (thiopropanal sulfoxide and diallyl disulfide) when cut, which can cause eye irritation, respiratory and cutaneous allergic reactions. As a result, onions, along with the rest of the Amaryllidaceae family, have been implicated as a cause of occupational rhinoconjunctivitis and bronchial asthma (6).

Molecular Aspects

Allergenic molecules

Table adapted from Allergome.org (9).

Allergen

Type

Mass (kDa)

All c 3

Lipid transfer protein

12

All c 4

Profilin

-

All c alliin lyase

Alliinase

56

The main allergens characterized for onion include All c 3 (a 12 kDa lipid transfer protein), All c 4 (a profilin), and All c Alliin lyase. The case report of anaphylaxis due to ingestion of cooked onion was likely due to the thermostable lipid transfer protein, All c 3 (2).

Cross-reactivity

Allergenic cross-reactivity has been demonstrated between members of the Amaryllidaceae family. Cross-reactivity with peach has been postulated, but findings indicate that this cross reactivity is marginal (2). 

Compiled By

Author: RubyDuke Communications

Reviewer: Dr.Michael Thorpe

 

Last reviewed: May 2022

References
  1. Singh A. Origin Area , Production ,Varieties, Package of Practices For Onion. 2019.
  2. Albanesi M, Pasculli C, Giliberti L, Rossi MP, Di Bona D, Caiaffa MF, et al. Immunological characterization of onion (Allium cepa) allergy. Postepy dermatologii i alergologii. 2019;36(1):98-103.
  3. Baloch A, Baloch S, Baloch S, Noor H, Badini S, Bashir W, et al. Economic Analysis of Onion (Allium cepa L.) Production and Marketing in District Awaran, Balochistan. 2014;5:192-205.
  4. M. Castillo (2020). "Allergic hypersensitivity to garlic and onion in children and adults." Allergologia et Immunopathologia 48(3): 232-236
  5. ITIS. Allium cepa  L. 2022.
  6. Armentia A, Martín-Armentia S, Pineda F, Martín-Armentia B, Castro M, Fernández S, et al. Allergic hypersensitivity to garlic and onion in children and adults. Allergologia et Immunopathologia. 2020;48(3):232-6.
  7. Almogren A, Shakoor Z, Adam MH. Garlic and onion sensitization among Saudi patients screened for food allergy: a hospital based study. Afr Health Sci. 2013;13(3):689-93.
  8. Arena A, Cislaghi C, Falagiani P. Anaphylactic reaction to the ingestion of raw onion. A case report. Allergol Immunopathol (Madr). 2000;28(5):287-9.
  9. Allergome. Onion 2021 [cited 2021 6.12.21]. Available from: http://www.allergome.org/script/search_step2.php.