A sore throat is often just one symptom of a bacterial or viral infection, such as the common cold.

The most common types of bacteria and viruses that may cause a sore throat include:

• the rhinovirus, coronavirus and parainfluenza viruses, which normally cause the common cold – these are responsible for a quarter of all sore throats
• different types of streptococcal bacteria – group A streptococcal bacteria cause 10% of sore throats in adults and nearly a third of sore throats in children, with groups C and G also thought to be a cause of sore throats

Other bacteria and viruses each tend to be responsible for less than 5% of sore throats. These include:

• types A and B of the flu virus
• adenovirus – which can also cause conjunctivitis, an infection in the eye
• herpes simplex virus type 1 – which normally causes cold sores
• the Epstein-Barr virus (EBV) – which normally causes glandular fever

There are many other, rarer, bacteria and viruses that are each responsible for less than 1% of sore throats.

Catching an infection

The bacterium or virus that causes a sore throat is usually caught from someone else who is already infected. For example, the common cold is spread through tiny droplets of fluid that contain the cold virus, launched into the air when someone coughs, sneezes or speaks.

If you breathe in one of these droplets or touch a surface that has the virus on it, and then touch your face, you may become infected.

Once you have caught an infection, two types of sore throat can develop. These are:

• pharyngitis – when the area at the back of your throat (the oropharynx) becomes inflamed
• tonsillitis – when your tonsils (the two lumps of tissue either side of your throat) become inflamed

Read more about treating a sore throat.

Non-infectious causes

Less commonly, sore throats can have non-infectious causes. These include:

• irritation caused by cigarette smoke or alcohol
• irritation from a nasogastric tube (passed down your nose and into your stomach to provide liquid food if you can't eat solid food)
• gastro-oesophageal reflux disease – a condition that causes acid to leak upwards from the stomach into the gullet
• Stevens-Johnson syndrome – a very severe allergic reaction to medication
• Kawasaki disease – a rare condition that affects children under five years of age
• allergies – such as hay fever (an allergic reaction to pollen or spores) which, in rare cases, may also cause a sore throat
• some blood disorders, such as leukaemia (cancer of the bone marrow) or aplastic anaemia (when the bone marrow does not produce enough blood cells)
• oral mucositis (inflammation of the layer of tissue that lines your mouth), which can be caused by radiotherapy or chemotherapy (cancer treatments)

Bone marrow
Bone marrow is the soft, spongy tissue in the centre of bones that produces blood cells.

Inflammation
Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.

Tonsils
Two small glands found at the back of your throat, behind the tongue.