Egg and Cow’s Milk Top the List of Food Allergens in Infants With Eczema in 16-Year Iranian Study

Infants with atopic dermatitis, the itchy, inflamed skin condition better known as eczema, are far more likely than healthy babies to react to the foods sitting on the family dinner table. A new retrospective study from Kashan, Iran, has now mapped exactly which foods trigger immune responses in these youngest patients, drawing on sixteen years of clinical records and one of the oldest diagnostic tools in allergy medicine: the skin prick test. The findings, published in Immunity, Inflammation and Disease, point to egg as the dominant culprit, followed closely by cow’s milk and tree nuts, and they carry practical weight for pediatricians who must decide whether to recommend dietary restrictions in a population where blanket food exclusions can do more harm than good.

The research team, based at the asthma and allergy clinic of Shahid Beheshti Hospital and affiliated with Kashan University of Medical Sciences, combed through electronic medical files from January 2005 to December 2021. Their inclusion criteria were strict: infants between six and twenty-four months of age with a diagnosis of atopic dermatitis and a completed skin prick test panel. Babies whose medications could not be safely paused, those with severe skin disease other than eczema, and any infant with a history of anaphylaxis to food were excluded, as were patients with incomplete records. After applying these filters, ninety-eight infants made it into the final analysis, a modest but carefully characterized cohort that received ethics approval and parental informed consent for every case.

The skin prick test itself deserves a technical word, because its simplicity belies the immunology it captures. Clinicians placed standardized extracts of eight common food allergens—milk, egg, tree nuts, soybean, wheat, seafood, rice, and peanut—onto a small scratch on the palm side of the infant’s forearm. Antihistamines and systemic steroids were halted a full week beforehand to avoid blunting the response. After fifteen to twenty minutes, the site was inspected: a wheal greater than three millimeters, accompanied by erythema exceeding eight millimeters, counted as positive. The researchers then graded reactions by size, treating wheals of three to five millimeters as mild, five to ten as moderate, and anything beyond ten as severe. The test works by detecting allergen-specific immunoglobulin E, or IgE, antibodies parked on mast cells in the skin; when the extract cross-links those antibodies, the cells dump histamine and other inflammatory mediators, producing the visible swelling within minutes.

The headline result was unambiguous. Egg allergy appeared in 64.3 percent of the infants, cow’s milk in 49 percent, tree nuts in 35.7 percent, soy in 20.4 percent, and wheat in 12.2 percent. Girls made up the majority of the cohort at 55.1 percent, and most babies—66.3 percent—had mild disease, with 24.5 percent moderate and only 9.2 percent severe. The average age at which eczema first appeared was just under six months, at 5.72 months, underscoring how early in life the disease and its dietary entanglements begin. Feeding history in the first half-year was also recorded: 63.3 percent of infants were exclusively breastfed, 13.3 percent received only formula, and the rest a combination of the two.

Two statistically significant patterns emerged from the cross-tabulations. First, egg allergy was markedly more common in girls than in boys, affecting 74.1 percent of female infants versus 52.3 percent of males, a difference the authors reported as significant at p equals 0.025. Second, cow’s milk allergy clustered in early-onset disease: 56.06 percent of infants whose symptoms began before six months of age were sensitized to milk, compared with 34.3 percent of those whose eczema appeared later, significant at p equals 0.044. Wheat sensitization showed a striking fivefold elevation in the early-onset group, 16.6 percent versus 3.1 percent, but the small numbers in each subgroup kept this from reaching statistical significance. Notably, the type of allergen bore no relationship to how the infant was fed in the first six months, nor to the severity of the eczema itself.

Severity did, however, track tightly with timing. Infants with severe atopic dermatitis had developed symptoms at an average age of just 2.78 months, compared with 7.17 months in the moderate group and 5.60 months in the mild group, a difference significant at p equals 0.014. This aligns with a broader clinical observation that the earliest and most aggressive presentations of eczema often mark children destined for the so-called atopic march, the progression from skin disease to food allergy, allergic rhinitis, and asthma. Immunologically, atopic dermatitis is driven by a skewed T helper 2 response, with interleukins IL-4, IL-5, and IL-13 ramping up IgE production and activating eosinophils and mast cells. When food antigens enter this primed environment, B lymphocytes pump out allergen-specific IgE, which arms mast cells and basophils via their Fc receptors; re-exposure then triggers the full allergic cascade.

The Kashan results sit within a patchwork of international findings that highlight how geography and diet shape allergen profiles. A Chinese study of nearly 1,700 children under two identified egg, shrimp, and fish as leading triggers, while Iranian work in Mashhad found egg white, egg yolk, and cow’s milk at the top of the list. In Bushehr, southern Iran, peanuts, walnuts, and soybeans dominated, and Czech researchers reported nuts, milk, and peanuts as the chief offenders among older patients. The authors of the new study attribute this variability to differences in dietary habits, culture, ethnicity, and age of the studied populations, along with a straightforward epidemiological principle: the more a population consumes a given food, the more likely its members are to become sensitized to it. Cow’s milk and egg, staples of infant diets nearly everywhere, recur as the leading allergens across most regions, including prior Iranian surveys.

Perhaps the most consequential implication of the study is what it says about feeding practices. The researchers found no association between breastfeeding, formula feeding, or mixed feeding and either allergen sensitization or disease severity, a result consistent with systematic reviews that have failed to demonstrate a clear protective or predisposing effect of exclusive breastfeeding on atopic outcomes. This echoes earlier Iranian work showing that breastfeeding patterns and the timing of complementary foods did not influence eczema incidence or severity. The practical message is twofold: infant feeding choices alone cannot explain allergic outcomes without accounting for genetic susceptibility and immune mechanisms, and clinicians should resist reflexively prescribing long lists of foods to eliminate from both mother’s and baby’s diets, a practice the authors note can produce what they describe as double starvation and injury. Precise identification of the offending allergen, followed by targeted avoidance, is the strategy that actually improves quality of life.

The study is candid about its limits. Its retrospective design depended on medical records rather than prospective enrollment, more than forty-five cases were dropped for missing data, and the skin prick test, while valuable, detects sensitization rather than clinically confirmed allergy. Without confirmatory serum-specific IgE measurements or oral food challenges, the true prevalence of food allergy may have been overestimated. Moreover, atopic dermatitis comes in two immunological flavors: the extrinsic, IgE-mediated form that prick testing captures well, and the intrinsic, non-IgE-mediated form, in which patients show classic eczema despite normal IgE levels and negative tests. The Kashan findings therefore largely reflect sensitization patterns in extrinsic disease and may underestimate food-related triggers in intrinsic cases. The authors call for prospective, multicenter studies with larger samples, standardized severity scoring, and confirmatory diagnostics such as oral food challenges to sharpen the picture.

Even with those caveats, the sixteen-year dataset delivers a clear clinical takeaway. Infants with eczema in this Iranian population were most frequently sensitized to egg, cow’s milk, and nuts; egg sensitization skewed female, milk sensitization skewed toward early-onset disease, and the earliest symptom onset predicted the most severe eczema. Because food sensitivity in many patients begins before six months of age, the authors recommend that highly allergenic items such as egg yolk and wheat not be introduced into infant diets before that age. In an era when allergic diseases of every type are rising worldwide, region-specific maps of allergen frequency like this one are becoming essential instruments for pediatricians navigating the fine line between protecting vulnerable infants and depriving them of nutrition they can safely tolerate.

Subject of Research: Food allergen sensitization patterns in infants with atopic dermatitis assessed by skin prick testing

Article Title: Assessment of Common Food Allergens in Infants With Atopic Dermatitis in Kashan From 2005 to 2021

Article References: Madani, S. R., Salehi, M., Arani, M. H., Shaterian, Z., Heidari, M. M., & Azadchehr, M. J. (2026). Assessment of Common Food Allergens in Infants With Atopic Dermatitis in Kashan From 2005 to 2021. Immunity, Inflammation and Disease, 14(10), Article e70544. https://doi.org/10.1002/iid3.70544

Image Credits: AI Generated

DOI: 10.1002/iid3.70544

Keywords: atopic dermatitis, food allergy, infants, skin prick test, egg allergy, cow's milk allergy, IgE, eczema, Iran, pediatric allergy, breastfeeding, atopic march