AbstractPolyethylene glycol (PEG), also known as macrogol, is an excipient in numerous medications, health care products, cosmetics, and foods. It acts as an inert bulking, or stabilizing, agent. Despite its ubiquity, including in 2 of the newly launched vaccines against SARS‐CoV‐2, awareness of PEG allergy remains low. We present 6 cases of acute hypersensitivity to PEG. Accurate diagnoses in these cases posed a challenge, and although the triggering agents differed, PEG was demonstrated as the common culprit. All cases were female, with a mean age of 36.4 years. Four patients were originally suspected to have nonsteroid anti‐inflammatory drug allergy, and 2 had a history of chronic spontaneous urticaria and angioedema. Biphasic allergic reactions featured prominently in this case series. Diagnosis relies on a high index of suspicion leading to a focused clinical history, supported by skin tests with PEG solutions to demonstrate sensitization. This case series highlights important clinical features of this rare, potentially serious, and increasingly recognized excipient allergy.