Pharyngitis is acute or chronic inflammation of the pharynx (the part of the throat that is situated between the tonsils and the voicebox), causing a sore throat.
The most common cause is a viral infection. Pharyngitis often occurs as part of a cold (see cold, common) or influenza. It may also be an early feature of glandular fever (infectious mononucleosis) or scarlet fever. Sometimes, the condition is due to a bacterial infection, such as a streptococcal infection; a rare but serious bacterial cause is diphtheria. Swallowing substances that can scald, corrode, or scratch the lining of the throat, smoking, and excessive consumption of alcohol may also be the causes of pharyngitis.
As well as a sore throat, there may be discomfort when swallowing, slight fever, earache, and swollen lymph nodes in the neck. In severe cases of pharyngitis, there may be a high fever, and the soft palate and throat may swell so much that breathing and swallowing can become difficult.
Gargling with warm salt water and taking analgesic drugs such as paracetamol (acetaminophen) or ibuprofen (Nurofen) is usually the only treatment needed. If the sore throat is severe or prolonged, a doctor may take a throat swab and prescribe antibiotic drugs (such as penicillin v).
See this article about upper respiratory infections which covers pharyngitis (and tonsillitis) in detail:
Upper respiratory tract infections in detail - technical
Laryngitis and pharyngitis - technical