Hydrolysate formulas (HF) have been developed with the goal of reducing the allergenicity of cow's milk (CM) proteins, thus providing a suitable formula for feeding babies with CM allergy (CMA). More recently, whey HFs have provoked 208 reactions in babies at high risk of atopy when given for CMA prevention. We report the clinical and immunologic findings of four babies apparentlly sensitized by a partially whey hydrolysate formula (PWHF) in the nursery. They were exclusively BM (breast

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... d by their mothers avoiding highly allergenic foods, but experienced anaphylaxis after a re-feeding with the PWHF. Sensitization to PWHF seems to have occurred in the first days of life. No baby suffered from allergic symptoms during BM-feeding. These case reports suggest that a PWHF may be allergenic not only in an already sensitized subject, but also sensitizing in a genetically predisposed baby being immunogenic in the IgE system. These data strongly indicate that maternal diets during BM-feeding, in two instances suggested by family doctors, are effective as a BM complement.