HRH1 and urticaria: H1R antagonists, also known as antihistamines, are a class of drugs used to treat allergic diseases like allergic rhinitis, allergic conjunctivitis, and urticaria.9 These drugs alleviate symptoms such as itching, swelling, and redness by blocking the action of histamine on the H1R. Despite significant progress in the GPCR photopharmacology field,10–13 and the high number of drugs targeting H1R,8 it has proven remarkably difficult to develop a photoswitchable ligand that effectively modulates this receptor.