Most cases of tonsillitis are caused by a viral infection.

Viruses known to cause tonsillitis include:

• rhinoviruses – which are viruses that cause the common cold
• the influenza virus
• parainfluenza virus – which causes laryngitis and croup
• enteroviruses – which cause hand, foot and mouth disease
• adenovirus – which is a common cause of diarrhoea
• the rubeola virus – which causes measles

In rare cases, tonsillitis can also be caused by the Epstein-Barr virus, which causes glandular fever.

If this is the case, you'll probably feel very ill. You'll have a sore throat and the lymph glands in your throat may be swollen. You may also have a fever and feel very tired.

Bacterial tonsillitis

Bacterial tonsillitis can be caused by a number of different bacteria, but it's usually due to group A streptococcus bacteria.

In the past, serious bacterial infections, such as diphtheria and rheumatic fever, have been linked with tonsillitis. However, this is now rare because these conditions are vaccinated against and treatment for them has greatly improved.

How tonsillitis is spread

Tonsillitis itself isn't contagious but the infections that cause it are.

Viruses, such as those that cause colds and flu, are spread through coming into close contact with someone who's infected.

When an infected person coughs or sneezes, the virus is contained in the millions of tiny droplets that come out of their nose and mouth. You can become infected by breathing in the contaminated droplets. This is known as direct contact.

You can also become infected if you touch a surface or object that the droplets have landed on and then touch your face. This is known as indirect contact.