A dental abscess occurs when bacteria infect and spread inside a tooth, your gums or the surrounding tissue.

Your mouth is full of bacteria, which combine with small particles of food and saliva to form a sticky film called plaque, which builds up on your teeth. Brushing your teeth helps to stop plaque from building up.

Eating and drinking food and drink high in carbohydrates causes the bacteria in plaque to turn the carbohydrates into the energy they need to reproduce. Acids are then produced, which leads to tooth decay.

Tooth decay can lead to the formation of a dental abscess. This can occur when bacteria spread into:

• the centre of a tooth (the pulp) through tiny holes in the tooth (dental caries) caused by the excess acid – when this spreads under the teeth this is known as a periapical abscess
• your gums and surrounding tissues – this is known as a periodontal abscess

Periapical abscesses

When a periapical abscess develops, plaque bacteria infect your tooth as a result of dental caries, which form in the hard outer layer of your tooth (the enamel).

Dental caries break down the enamel and the softer layer of tissue underneath (dentine), eventually reaching the centre of the pulp. This is known as pulpitis. The dental pulp in the middle of the tooth dies and the pulp chamber becomes infected.

The bacteria continue to infect the pulp until it reaches the bone that surrounds and supports your tooth (alveolar bone), where the periapical abscess forms.

Periodontal abscesses

A periodontal abscess is caused by gum disease (also known as gingivitis or periodontitis).

A periodontal abscess may also occur as a result of:

• gum damage, even if you do not have periodontitis
• smoking and using smokeless tobacco – read more information about quitting smoking

Risk factors

Risk factors for a dental abscess include:

• poor oral hygiene – if you do not brush your teeth and floss regularly, your risk of developing a dental abscess increases
• having a diet high in sweet and sticky food and drink – such as chocolate, sweets, sugar and fizzy drinks and/or starchy foods, such as crisps, white bread, pretzels and biscuits
• having a weakened immune system – this may be because of an underlying health condition, such as diabetes, or the side effects of treatments like steroid medication (corticosteroids) or chemotherapy

Read more about the risks of gum disease.