Mastocytosis is a group of disorders characterized by the accumulation of mast cells in various tissues. In this article we report an interesting case of cutaneous mastocytoma in a 3-month-old infant. We describe two episodes characterized by an exacerbation of the skin lesion with the typical Darier’s sign. Both of them occurred after breastfeeding. In both episodes, the mother had eaten shrimps before the breastfeeding. This peculiar case, difficult to understand regarding its pathogenesis, was successful resolved just with dietary prescription given to the breast feeding mother.