Peanut protein is secreted into breast milk of lactating women following maternal dietary ingestion. Exposure to peanut protein during breastfeeding is a route of occult exposure that may result in sensitization of at-risk infants.

Urticaria is a common disorder affecting one-fifth of the world's population. The pathophysiology is characterized by an increased propensity for mast cell degranulation with the release of potent mediators into the dermal and subdermal tissues with resulting vasoactive, chemotactic, and inflammatory effects. The final clinical manifestation of the typical urticarial lesion is the effect of several diverse effects and causes. The general classification is acute, chronic, and physical urticaria. In general, allergenic triggers can be identified in between 60-80% of acute urticarias. Physical urticarias are characterized by the onset after the specific inciting stimulus, which can reproduce the characteristic lesion which is usually of shorter duration (with the exception of delayed pressure urticaria). Chronic idiopathic urticaria is associated with thyroid autoimmunity and, more recently, anti-mast cell receptor antibodies. An extensive work-up is usually not indicated or helpful in identifying a cause. Food or other allergens are rare causes of this type of presentation. The evaluation and work-up is dependent on clues identified by history. The treatment is removal of specific and non-specific triggers and the use of symptomatic medications generally attenuating the mediator effects.