Why do I get a sore throat from sleeping with my mouth open?

Your throat was built to be watered by air that arrives warmed, filtered, and humidified through the nose. Sleep with your mouth open and you skip all of that: eight hours of dry, room-temperature air moving straight over the throat lining dries and irritates it, and you wake with a raw, scratchy throat that improves through the morning as normal swallowing and nasal breathing resume. That daily-fading pattern is the tell. The real question is why your mouth opens at night, and the answer is usually a nose that will not carry the load: a cold, allergies, a deviated septum, or enlarged turbinates all push breathing to the mouth, and the NHS notes congestion is swollen lining tissue - lying down makes it pool. Snoring and mouth breathing travel together, and so do sleep apnoea and mouth breathing, so loud snoring plus a dry, sore morning throat plus daytime tiredness is a combination worth mentioning to a GP. What helps: treat the nose (saline rinses, a steroid spray if allergies are in the mix), prop yourself up slightly, keep the bedroom air moist - the NHS suggests bowls of water where central heating dries the air - and skip evening alcohol, which relaxes the airway and worsens both snoring and mouth opening. A sore throat that persists all day, lasts over a week, or comes with white patches, fever, or a neck lump needs a GP, per the NHS sore throat guidance. Pymander is a free AI doctor, 24/7 by text, that can help you work out which fix is yours.