Carrot (Daucus carota) is one of the most important, widely cultivated root vegetables, belonging to Apiaceae family with a rank in the top 10 vegetables around the world. The most widely cultivated species of carrot include D. carota L. subsp. sativus with Central Asia to be considered as the origin. They are classified as eastern and western carrots based on the pigmentation of the roots with colors ranging from orange, yellow, purple, red and white. The fleshy edible taproots of carrots may be allergic to some individuals. Carrot sensitization was found wide across Europe and even in the USA, Mexico, and certain countries of Asia. Carrot is one of the prominent triggering vegetables for pollen-food-allergy-syndrome associated with birch and mugwort pollens. Ingestion can trigger oral allergy syndrome or pollen food allergy syndrome with symptoms ranging from swelling of lips, tongue and throat, nausea, dysphonia, itching of the nose and ear to even systemic reactions like anaphylaxis in some. Dau c 1 reported as a major allergen, out of the 4 allergens, which is homologous to Bet v 1, the birch pollen allergen. Carrot allergens are highly cross-reactive with especially birch tree pollens and celery. The allergy might be prevented in carrot sensitized people by avoiding any intentional or un-intentional consumption of carrot.

Nature

Carrot (Daucus carota) is one of the most important root vegetables in the Apiaceae family and is widely cultivated around the world with a rank in the top 10 vegetables (1, 2). It is a biennial erect herbaceous plant with 20-50 cm tall during the mature vegetative stage and 120-150 cm tall when flowering (3). The part of the plant that is mostly consumed is the roots due to its richness in carotenoids, anthocyanins, dietary fiber, vitamins and other nutrients (2). Carrot plants flowers in the second year of growth. Carrot flowers are flattened umbrella-shaped umbel and usually white in color. The leaves of the carrot plants are glabrous, green compound leaves growing in a rosette (2).

Habitat

Carrot is found in both wild and cultivated types. Wild carrot is a weed and can spread very fast. The cultivated carrot is mostly used as a vegetable. Carrot grows in natural grasslands or cultivated lands (3).

Taxonomy

The taxonomic classification of the genus Daucus is not clear. Earlier studies subdivided the genus into 5 sections of 20 species with Daucus L. as one having 12 species. D. carota subsp. carota is the best-known wild species among them. The most widely cultivated carrot includes D. carota L. subsp. sativus domesticated from wild species (4). Spooner et. al., performed a multivariate analysis among D. carota species and proposed to classify all of the known subspecies under two main subspecies as D. carota subsp. carota and subsp. gummifer (4, 5). The cultivated carrots are classified into eastern carrots and western carrots based on the pigmentation of roots. Eastern carrot roots are branched, purple or yellow in color due to the presence of anthocyanin with slightly dissected leaves. Western carrot roots are unbranched, orange-red or white in color due to the presence of carotene with highly dissected leaves (2).

Worldwide distribution

Most of the carrot allergic persons are reported to be sensitive to birch or mugwort pollens (6). A survey regarding triggers and symptoms of food allergy was conducted in Germany on 73 patients with a history of birch pollen associated food allergy. The results reported that the carrot was responsible for eliciting allergic reactions in 52% of patients (7). According to a EuroPrevall analysis (the study about the basis and prevalence of food allergy across Europe), 3.6% prevalence of sensitization to carrot was observed in a study on 4522 adults (aged 20-39 years) from 13 countries across Europe (8). Apple, banana and carrot were triggering foods for 5% of pollen food allergy syndrome (PFAS) due to birch and ragweed pollens in 122 children (0-18 year) in the USA (9), whereas, apple, peach and carrot were triggering foods for 26.7% of PFAS due to birch, grass and ragweed pollens in Croatia including 120 patients (10). A total of 2633 Mexican subjects were tested for food allergy through immunoglobulin E (IgE) positivity and carrot was found as food with high positivity in 37.5% of subjects although less than 50 samples tested (11).

A prevalence study of self-reported food allergy (FA), food sensitization (FS) and probable FA (individuals having symptoms plus IgE sensitization) to 24 Europrevall priority foods in adults (12) and in school-age children across Europe (13) was conducted to analyze geographical variation. Probable FA to carrot was markedly common among adults in Zurich, Switzerland (1.0 %) than in other countries of Europe (12). Carrot constituted 1.1% of 16,935 children (7-10 years old) for self-reported FA. Carrot along with hazelnut, apple and celery were important sources of FA in children in Central and Northern Europe. Carrot was among the most common sensitizing food in children causing probable FA in birch-endemic countries, Switzerland, Netherlands, Poland and Lithuania, maybe due to cross-reactivity with birch PR-10 protein (13). The prevalence of FS for carrot in the total study population (2196 patients) with available food serology was found to be 12.4% in Zurich, 8.3% in Madrid, 4.8% in Athens, 7.2% in Utrecht, 4.5% in Vilnius, 5.0% in Lodz and 2.1% in Reykjavik. Carrot was the cause of self-reported FA and matching FS in 30.3% of the total of 1989 subjects with available food serology (13).  

A similar study was conducted in South India for the 24 Europrevall priority foods in 11,791 adults (20-54 years), however, the South-Indian population was not found to be allergic to carrot as compared to high sensitization in Europe (14). According to a study conducted in China, India and Russia for 24 Europrevall priority foods in 35,549 school children (6-11 years), 1.5% subjects in Hongkong, 0% in Guangzhou, 2.0% in Shaoguan, 2.5% in Tomsk and 6.7% in India depicted positive serum specific IgE to carrot. However, only 0.15% of subjects in Russia reported symptoms with positive IgE, while others countries were not found to have a probable food allergy to carrot (15).

Risk factors

Carrot is considered to be one of the prominent triggering vegetables for pollen-food-allergy-syndrome (PFAS) associated with birch and mugwort pollens (10).

Living environment

Carrot adapts and grows in a cool climate and can be sown in spring in temperate zones or in winter in subtropical zones (2). It grows well at altitudes of 700 m in tropical regions with an optimum temperature of 16-24ºC and grows best in well-drained fertile soil with sandy texture and pH of 6.0 to 6.5 (3).

Worldwide distribution

Central Asia is considered to be one of the origins of cultivated carrot with Afghanistan to be thought as the first center of diversity and Turkey as the second center (2). Its cultivation has spread throughout the world and is now native to temperate regions of Europe, Southwestern Asia, and North Africa. It is also grown in North America, Japan, New Zealand and Australia (3). 

Main

Ingestion of carrot can trigger food related allergic response as Oral Allergy Syndrome (OAS) or Pollen food allergy syndrome (PFAS) (16-19).

Food Allergy

Carrot is normally associated with food allergy and OAS or PFAS (Sánchez-Guerrero et al, 2020). Allergic symptoms in OAS mostly include the oropharyngeal regions such as swelling of lips, tongue, and throat, nausea, dysphonia, and itching of the nose and ear (17, 20). About 50% of carrot allergic patients develop systemic reactions (6). In a study on 55 patients with airborne allergy, food hypersensitivity (mainly OAS) was reported in 15 patients especially with apples, carrots, cherry, peach, hazelnut, walnut, celery and nectarines (21). Systemic allergic reactions are reported after the ingestion of carrot in pollen allergic patients due to cross-reactivity (22). PFAS was found to be significantly correlated with root vegetables including carrot in a study conducted on 54 seasonal allergic rhinitis patients (23).

Allergic rhinitis

A study on 2305 representative samples of the Korean population found that more carrot consumption (OR - 2.01; CI, 1.01–1.43; p - 0.10) was associated with increased risk of allergic rhinitis (24). A study enrolled 54 patients with seasonal allergic rhinitis and subjected to skin prick tests and microarray analysis to determine the incidence of PFAS and food tolerance. Carrot showed a positive skin prick test in 29 patients (23).

Asthma

Some patients presented asthma due to handling or ingesting raw carrots which were due to major carrot allergen Dau c 1 according to a small study. 2 patients were found to be sensitized to carrots directly without pollens involved while 1 patient has pollen-related carrot allergy (25).

Atopic Dermatitis

Allergic contact dermatitis by Apiaceae root vegetables is rare, however; few cases of dermatitis have been reported due to carrots (26-28).

Other diseases

Anaphylactic shock has been reported in some case studies in carrot allergic patients (17, 29, 30).

Other topics

As per a study, carrot was the food trigger for PFAS in 15.5% of adults with eosinophilic esophagitis (31).

Prevention strategies

Avoidance

The major management of carrot allergy in pollen sensitized individuals is to avoid eating the food which poses a positive challenge (22). 

Author: Turacoz Healthcare Solutions

Reviewer: Dr. Fabio Iachetti

Last reviewed: November  2020