An allergy prevention method and system. The method includes retrieving, by a computing system from a fidelity card, a user profile comprising information specifying first elements known to cause a user to have an allergic reaction. The computing system retrieves data associated with an item for purchase. The data comprises information specifying second elements comprised by the item. The computing system compares the first elements to the second elements to determine that a first element of the first elements matches a second element of the second elements. The computing system generates and presents to the user, a warning indicating that the first item may cause the user to have an allergic reaction.