Oat
Summary
Oats are small cereal grains rich in fiber and antioxidants and possess various health benefits. It belongs to the genus Avena. Oats are used as cereal, fodder, hay, straw beds, grains, etc. They are more popularly consumed in Europe and are a source of food allergy. Ingestion of oat cereal or inhalation of oat flour has been reported to cause allergic reactions in sensitive individuals.
Clinically, oat allergies are reported to cause Oral Allergy Syndrome (OAS), anaphylaxis, gastro-intestinal symptoms, skin reactions, and respiratory symptoms such as rhinitis, rhino-conjunctivitis, and asthma in sensitized individuals. Children with atopic dermatitis constitute a risk group of developing epicutaneous sensitization to oats and subsequently acute allergies on using oat-containing cosmetics.
Allergens in oats haven’t yet been characterized but various studies have shown different IgE- binding proteins from oats. Cross-reactivity between gliadins from wheat and hordeins in barley, avenins from oats, coixins in Job’s tears, and secalins from rye has been observed. Additionally, cross-reactivity has been demonstrated between rice, millets, oats, and grass pollen.
Avoidance of oats is suggested as a preventative strategy against the allergic reaction caused by oat.
Epidemiology
Worldwide distribution
Food allergies with oat are not commonly reported, especially in Asian countries where oats are not as popularly consumed as in European countries.
A cross-sectional study with 365 allergic Honduran children (age ranging from 1 to 18 years) showed positive skin prick test (SPT) for oats in 3% (11 out of 365) participants.
Worm et al. (2006) extracted a random sample of 13,300 Germans out of which 408 self-reported the prevalence of atopic dermatitis (AD). AD was confirmed in 146 individuals out of which 111 were clinically examined and 28 were diagnosed with active eczema lesions. Among them, 14.8% had a positive skin prick test (SPT) to oatmeal and barley flour.
Boussault et al. (2007) conducted an extensive study on oat sensitization in children with AD in France. The study showed that out of 302 children, 98 (32.5%) were sensitized to oat and among them, 19.2% (58/302) were positive to oat in SPT and 14.6% (44/302) in Atopy patch test (APT).
A study evaluated the prevalence of oat allergy in children diagnosed to have wheat allergy in Maryland, USA. Out of 185 wheat allergic patients, 10% reacted to oat extracts.
Risk factors
In children with AD, the application of oat-containing emollients can put them at a high risk of developing epicutaneous sensitization which can further lead to acute food allergies.
Route Of Exposure
Main
Ingestion/consumption of oat cereal can elicit an allergic response.
Secondary
Inhalation of oat flour or dust can cause allergic responses.
Clinical Relevance
Oral allergy syndrome and Anaphylaxis
Oats have been found to be linked with the cases of oral allergy symptoms. Oat-related food allergies may be induced through the gastrointestinal (GI) tract and skin. Contact allergy to oat protein present in moisturizers has also been reported. Anaphylaxis associated with oat allergy has also been reported in a few studies.
A 14-year old boy with a history of AD and recurrent croup was presented with pruritus on the pharynx, hands and feet, and facial erythema immediately after drinking oat milk. Previously he also developed oral pruritus upon consumption of oats; however, he was able to tolerate other cereals and even wheat. Another patient, a 62- year old man with a history of ischemic heart disease developed anaphylaxis after ingestion of oat milk. He complained of oropharyngeal pruritus, dyspnea, dysphonia, followed by generalized acute urticaria within 5 minutes of consuming oat milk. He didn’t exercise before taking food and didn’t take any nonsteroidal inflammatory drug (NSAIDs) and no probable triggering cofactors for this severe reaction were identified. He couldn’t tolerate oats but can tolerate other types of cereals.
A 7 -year old boy presented with cough, wheezing, and pruritus within 30 minutes of ingesting wheat and oats cereal. He had no previous allergy records and consumed oats for the first time. His serum specific IgE (sIgE) test was higher for oats compared to wheat. These oat specific IgE levels, the reactivity of serum IgE to oat protein and no history of food allergy indicated that the patient may be allergic to oat.
A case reported anaphylaxis in an adult male on ingestion of oat milk. This 70-year old man with a past medical history of hypertension and rheumatoid arthritis was presented with an acute episode of palmoplantar pruritus, generalized exanthema, vomiting, nausea, dysphonia, laryngeal and thoracic oppression and hypotension within 10 minutes of ingesting oat milk. He didn’t have an allergy to any other cereal (cross-sensitization to other cereals was absent) and the sensitization was due to oat milk ingestion.
Mendonca et al. (2016) reported about a patient who developed angioedema minutes after consuming oatmeal cookies. On subsequent exposures to oat, the patient presented with rash, angioedema and dyspnea.
In another case, a 23- year old Japanese woman with a history of AD and bronchial asthma developed general urticaria and dyspnea within 30 minutes of consuming granola containing oats; her symptoms disappeared within several hours with an antihistamine.
Cereal- dependent exercise-induced anaphylactic response was observed in a 37-year old woman. On diagnosis, she showed positive SPT to wheat, barley and oats.
Allergic rhinitis and rhino-conjunctivitis
Since a long time, the allergic response such as rhinitis and Baker’s asthma due to inhalation of proteins from oat and cereal flour and dust has been known. Pala et al. (2010) reported a case of a 30- year old atopic man complaining of seasonal rhino-conjunctivitis. Since the time he started working as a cereal stocker, he complained of sneezing, chest tightness, dry coughing and wheezing, especially on handling cereal seeds like oats, millets, and Phalaris canariensis (a seed used as bird feed). His symptoms were seen on immediate exposure to the allergen and disappear in the absence of exposure.
Asthma
Boussault et al. (2007) studied the prevalence and risk factors associated with oat sensitization in children with a history of AD and found that two out of five patients with positive challenge tests to oats showed symptoms like repeated coughing fits in one and mild asthma attack in other, one developed facial erythema and pruritus and one case showed aggravation of atopic dermatitis lesions. Two patients complained of vomiting, diarrhea and pain in the abdomen. One of the patients presented with both respiratory and cutaneous symptoms.
In one case report, a patient was presented with itching upon using a moisturizer containing oatmeal and years later he reported developing urticaria, vomiting and angioedema upon ingestion of milk, mixed cereals and fruits.
Prevention And Therapy
Prevention strategies
Avoidance
Avoidance of the particular causative allergen in food allergies is currently the only treatment and avoidance of oats is recommended as a part of multiple-food exclusion. In an extensive study of the prevalence of oat allergy in children with AD, a correlation was found between repeated use of cosmetics with oat extracts and food allergy to oats and was suggested to avoid using oat extract containing skincare products (emollients) in children with AD. EU labeling law states the mandatory declaration of oats and other cereals containing gluten (wheat, rye and barley) on the labels of the food items.
Cross-Reactivity
Cross-reactivity between gliadins from wheat, hordeins from barley, avenins from oats, coixins in Job’s tears, secalins from rye has been observed. A study involving 10 patients (6 girls, 4 boys) aged between 5-15 years with a history of hypersensitivity after wheat consumption was evaluated to see cross-reactivity with other cereals including barley and oats. The cross-reactivity rate to oats was found to be 33.3% (3/9). The study also concluded that IgE mediated reaction to oat may be due to allergens different from wheat gliadin and glutenin extracts.
Another research demonstrated the cross-reactivity between millets, rice, corn, and other cereals. Out of 5 patients with positive SPT to millets, 3 patients showed positive SPT to oats, corn, rice, wheat, rye and barley.
Sensitization to oats was observed in flood-tolerant, grass pollen allergic patients. Out of 65 subjects, 11 showed sensitization to one or more cereals from oats, maize or rice (Group II).
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