Tonsillitis is an inflammation of the tonsils, which are two oval-shaped pads of tissue at the back of the throat, one tonsil on each side. The most common cause of tonsillitis is a viral infection, such as the viruses that cause the common cold or flu virus (influenza) . However, bacterial infections can also cause tonsillitis, with the most common bacterium being Streptococcus pyogenes (group A streptococcus), which is the bacterium that causes strep throat. Other strains of strep and other bacteria can also cause tonsillitis.

The tonsils are the immune systems first line of defense against bacteria and viruses that enter the mouth, which makes them particularly vulnerable to infection and inflammation. Tonsillitis is most common in children, teenagers, and young adults, and it is more common in children ages 5 to 15. Risk factors for tonsillitis include young age, frequent exposure to germs, and having a weakened immune system.

Symptoms of tonsillitis include swollen tonsils, sore throat, difficulty swallowing, tender lymph nodes on the sides of the neck, fever, headache, loss of appetite, ear pain, and swollen glands in the neck or jaw. In children, symptoms may also include upset stomach, vomiting, stomach pain, drooling, and not wanting to eat or swallow.

Treatment for tonsillitis depends on the cause. If the cause is a viral infection, there is no medicine to treat it, and the symptoms usually go away on their own within a week. If the cause is a bacterial infection, such as strep throat, antibiotics may be prescribed. Other treatments include getting plenty of rest, drinking plenty of fluids, eating soft foods, and taking over-the-counter pain relievers.