Egg allergy sensitized 64.3 percent of infants with atopic dermatitis in a 16-year retrospective study of 98 patients seen at Shahid Beheshti Hospital in Kashan, Iran, between January 2005 and December 2021. Cow's milk followed at 49 percent, with tree nuts at 35.7 percent, soy at 20.4 percent, and wheat at 12.2 percent. The findings, published in Immunity, Inflammation and Disease, position egg as the dominant food allergen in this eczema cohort and reinforce the case for targeted, not blanket, dietary restrictions.

What did the study actually measure?

The team drew from electronic medical files of infants aged 6 to 24 months with a confirmed atopic dermatitis diagnosis and a completed skin prick test panel. Researchers excluded babies whose medications could not be safely paused, those with severe non-eczema skin disease, infants with prior food anaphylaxis, and any patient with incomplete records. Of 143 candidates screened, 98 made it into the final analysis. Girls comprised 55.1 percent of the cohort. Most had mild disease (66.3 percent), with 24.5 percent moderate and 9.2 percent severe. Mean age at eczema onset was 5.72 months.

How did the skin prick test identify sensitization?

Clinicians applied standardized extracts of eight common food allergens—milk, egg, tree nuts, soybean, wheat, seafood, rice, and peanut—to a forearm scratch. They paused antihistamines and systemic steroids for one week before testing to avoid blunting the response. After 15 to 20 minutes, the team graded reactions by wheal size: 3 to 5 mm as mild, 5 to 10 mm as moderate, and greater than 10 mm as severe. Erythema exceeding 8 mm with a wheal of 3 mm or more counted as positive. The test detects allergen-specific IgE antibodies on cutaneous mast cells; cross-linking by the extract triggers histamine release and visible swelling within minutes.

What patterns linked allergens to sex, timing, and severity?

Egg sensitization skewed female, affecting 74.1 percent of girls versus 52.3 percent of boys (p = 0.025). Cow's milk clustered in early-onset disease: 56.06 percent of infants whose eczema appeared before six months reacted to milk, compared with 34.3 percent of those with later onset (p = 0.044). Wheat sensitization showed a fivefold elevation in the early-onset group (16.6 percent versus 3.1 percent), though the small subgroup numbers kept the finding from reaching statistical significance. Neither allergen sensitization nor disease severity correlated with the type of feeding in the first six months.

Severity, however, tracked tightly with timing of onset. Infants with severe atopic dermatitis had developed symptoms at a mean age of 2.78 months, compared with 7.17 months in the moderate group and 5.60 months in the mild group (p = 0.014). The pattern echoes the broader clinical concept of the atopic march, in which early aggressive eczema often precedes food allergy, allergic rhinitis, and asthma. Immunologically, atopic dermatitis reflects a skewed T helper 2 response, with IL-4, IL-5, and IL-13 driving IgE production and activating mast cells and eosinophils.

How do these findings fit the global picture?

The Kashan data align with international reports that 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 atop the list. In Bushehr, southern Iran, peanuts, walnuts, and soybeans dominated; Czech researchers reported nuts, milk, and peanuts as the chief offenders among older patients. The authors attribute the variability to dietary habits, culture, ethnicity, and the principle that the more a population consumes a food, the more likely it is to become sensitized to it. Cow's milk and egg, staples of infant diets globally, recur as leading allergens across most regions.

What does this mean for feeding guidance?

The practical takeaway, the authors wrote, is that infant feeding choices alone cannot explain allergic outcomes without accounting for genetic susceptibility and immune mechanisms. Clinicians should resist reflexively prescribing long food-elimination lists to mothers and babies, a practice that risks what the authors describe as double starvation and injury. The study found no association between exclusive breastfeeding, formula feeding, or mixed feeding and either allergen sensitization or disease severity, consistent with systematic reviews that have failed to demonstrate a clear protective effect of exclusive breastfeeding on atopic outcomes. Precise identification of the offending allergen followed by targeted avoidance improves quality of life.

What are the study's limitations?

The retrospective design relied on medical records rather than prospective enrollment. More than 45 cases were dropped for missing data. The skin prick test detects sensitization, not clinically confirmed allergy, and the study lacked confirmatory serum-specific IgE measurements or oral food challenges. Atopic dermatitis also splits into extrinsic, IgE-mediated disease, which prick testing captures well, and intrinsic, non-IgE-mediated eczema, in which patients show classic lesions despite normal IgE and negative tests. The Kashan results therefore reflect sensitization 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.

The study's clinical message crystallizes around timing. Because food sensitivity in many of these infants began before six months of age, the authors recommend that highly allergenic items such as egg yolk and wheat not be introduced before that threshold. As allergic diseases continue to rise worldwide, region-specific allergen maps like this one will become essential instruments for pediatricians balancing the line between protecting vulnerable infants and depriving them of nutrition they can safely tolerate.