Tonsillitis is a disorder involving inflammation of the tonsils. There are two tonsils, situated on either side of the back of the throat and they form part of the body's immune system. They, like the rest of the immune system, contain special cells to trap and kill bacteria and viruses travelling through the body. When the main site of infection is within the tonsils they swell, become red and inflamed and may show a surface coating of white spots.

Tonsillitis is extremely common in children and young people but it can occur at any age. The characteristics of the disease are pain in the throat and trouble swallowing. Tonsillitis is usually a self-limiting condition, ie it gets better without treatment, and generally there are no complications.

• Pain in the throat (sometimes severe) that may last more than 48 hours and be associated with difficulty in swallowing. The pain may spread to the ears.
• The throat is reddened, the tonsils are swollen and may be coated or have white spots on them.
• Possibly a high temperature.
• Swollen lymph glands under the jaw and in the neck.
• Headache.
• Loss of voice or changes in the voice.

If the sore throat is due to a viral infection the symptoms are usually milder and often related to the common cold. If due to Coxsackie virus infection, small blisters develop on the tonsils and roof of the mouth. The blisters erupt in a few days and are followed by a scab, which may be very painful.

If the sore throat is due to a streptococcal infection, the tonsils often swell and become coated and the throat is sore. The patient has a temperature, foul-smelling breath and may feel quite ill.

These different appearances are however very variable, and it is impossible to tell by looking at someone's throat whether the infection is due to a virus (which cannot be helped by antibiotics) or a bacterial infection (which might be helped by antibiotics).