First and foremost in frequency are viruses. Many viruses, and even those that cause mononucleosis (mono) and influenza (the flu), cause a sore throat. Some viruses can also produce painful blisters in the mouth and throat (aphthous stomatitis).
A sore throat can also be caused by bacteria. The two most common bacteria that cause sore throat are Streptococcus (strep throat) and Arcanobacterium haemolyticum (which causes sore throats mainly in young adults and is sometimes associated with a fine red rash).
The causes of sore throat range from trivial to grave. Breathing through the mouth dries the throat and makes it feel sore.. A sore throat that lasts for more than 2 weeks can be a sign of a serious illness, such as throat cancer or AIDS.
Throat soreness is typically associated with painful swallowing. Inflammation of the pharynx (pharyngitis) is the most common form of sore throat. Salt water gargles, hard candies, sprays (for example, Chloraseptic) and lozenges can provide temporary pain relief. A humidifier may help relieve sore throats caused by mouth breathing and dry air. Acetaminophen such as Tylenol or ibuprofen such as Advil may help control the pain. For adults, nasal sprays, such as Afrin, may be used for 2-3 days to prevent mouth breathing. Other decongestant products, such as Sudafed, may be also helpful.
Strep throat is a major concern. 5%-10% of sore throats in adults and 15%-40% of sore throats in children are caused by strep. A "rapid strep" test is often done and may be followed by a strep culture. If either is positive, the sore throat needs to be treated with penicillin or another antibiotic. The major objective is to prevent the development of rheumatic fever, a serious illness that can cause joint pain and heart valve damage.