Peanut allergy

An allergic reaction to substances from peanuts which leads to vomiting, diarrhea, cramps or in severe cases anaphylactic shock (a rapid restriction of the airways in combination of a drop in blood pressure, which can result in death within minutes). There is no cure, and affected people have to avoid contact with peanuts at all costs. In case of an allergic reaction, epinephrine can be injected as a first aid measure.

Howard is allergic to peanuts and takes care that there are no traces of peanuts in his food, especially when the guys eat Thai food (0102, 0116, 0220). Leonard mentioned that every Thai restaurant in town would know that and welcome him with "ah, no-peanut boy" (0116). However, when Penny offers to introduce Howard to one of her friends if he did her a favour, he eats a peanut-containing muesli bar and suffers from a severe allergic reaction, showing swelling of his entire face (angioedema) and respiratory problems (The Peanut Reaction).