Pain when swallowing, medically called odynophagia, can happen due to a variety of causes such as infections, inflammation, injuries, or obstruction in the throat or esophagus. Common causes include viral or bacterial infections like strep throat, tonsillitis, or a cold/flu which cause inflammation and soreness. Other causes are acid reflux (GERD), sinus infections, throat injuries from hot or spicy foods, and esophageal conditions like esophagitis or spasms. Essentially, the pain arises because inflamed or injured tissues in the throat or esophagus rub against each other during swallowing, causing discomfort or sharp pain.