A class of beta-lactam antibiotics differing from the penicillins in having a 6-membered, rather than a 5-membered, side ring. Although cephalosporins are among the most commonly used antibiotics in the treatment of routine infections, and their use is increasing over time, they can cause a range of hypersensitivity reactions, from mild, delayed-onset cutaneous reactions to life-threatening anaphylaxis in patients with immunoglobulin E (IgE)-mediated allergy.