Sheep Rennet Food Allergy in a Child With Atopic Dermatitis: A Case Report

Rennet allergy is uncommon and has historically been described primarily as an occupational allergy among individuals with substantial exposure to powdered rennet, particularly cheese makers.We report a pediatric patient with atopic dermatitis who developed anaphylaxis following ingestion of Parmesan cheese containing sheep rennet, despite having previously tolerated Parmesan and other dairy products.Detailed review of the patient's exposure history revealed regular application of a goat milk-containing lotion for several years as part of the management of atopic dermatitis, raising concern for cutaneous sensitization to animal-derived proteins with subsequent cross-reactivity to sheep rennet.Allergy evaluation was performed using skin-prick testing and measurement of serum specific IgE to sheep rennet.The combination of the clinical history and positive allergy testing supported a diagnosis of IgEmediated hypersensitivity to sheep rennet as the likely cause of the patient's anaphylactic reaction.The absence of a prior clinical reaction to Parmesan, together with the history of prolonged topical exposure to goat milk proteins on an impaired skin barrier, suggested that sensitization may have occurred through repeated cutaneous exposure to the goat milk lotion.This case demonstrates a rare presentation of anaphylaxis to sheep rennet in a child without occupational exposure and highlights a potential route of sensitization through topical exposure to animal milk proteins in the setting of atopic dermatitis.It underscores the importance of evaluating lesser-known ingredients, including processing agents, when investigating food-associated anaphylaxis, particularly when reactions occur to previously tolerated foods.This observation also raises awareness of the potential for cutaneous exposure to food-derived proteins in topical products to contribute to sensitization and subsequent systemic allergic reactions.