Sometimes a bacterial infection can cause pus to collect in a localised area just below the skin. When a pocket of this pus forms in the breast it is known as a breast abscess. It can be painful and requires urgent medical treatment to avoid complications.

How does a breast abscess form?

If bacteria get into the breast tissue, the immune system will send white blood cells to fight off the infection. During the process, some of the affected tissue can die, leaving a pocket that is gradually filled by pus, a mixture of white blood cells, dead tissues and bacteria. As the pocket fills up and swells, it forms into a painful, swollen lump known as an abscess.

Breast abscesses most often occur in women between 18 and 50 years old, especially if they are breastfeeding. There are two categories of breast abscesses:

• Lactational (puerperal) abscess: Forms in the peripheral areas of the breast, usually in the upper and outer sections
• Non-lactational abscess: Located in the subareolar (the coloured area around the nipple) or lower sections of the breast

A breast abscess is often a serious complication of mastitis in this case it is referred to as a lactational abscess. It can occur in the milk ducts that carry milk towards the nipple in a breastfeeding woman. Mastitis occurs when the breast produces more milk than the baby consumes and the extra milk backs up within the breast. When this happens, normally harmless bacteria in the milk duct grow more rapidly, triggering a response from the immune system. If mastitis is untreated, an abscess can form in one or more of the affected milk ducts. Breastfeeding women who are more than 30 years old, breastfeeding their first baby, or whose pregnancy lasted 41 weeks or more are more at risk of developing a lactational breast abscess.

In non-breastfeeding women, bacteria can enter the breast through a cracked or sore nipple - this is a non-lactational abscess (though it can happen in breastfeeding women too).

Having a history of previous mastitis, smoking, diabetes, HIV infection or undergoing immunosuppressive therapy can put a woman more at risk of developing a breast abscess. Having a nipple piercing can also increase a woman's risk.

How to know if a breast lump is an abscess?

If you have a breast abscess you will have a painful tender lump in the breast that is red and feels hot, and the surrounding skin may be swollen. You may have a high temperature, or fever, and feel generally unwell.

If the lump has regular borders and is smooth, and feels solid or like a cyst, it may be an abscess.

Regardless of if you think you have a breast abscess or it is another type of lump, if you have a lump in your breast it is important that you seek medical advice urgently, to rule out other conditions such as breast cancer and also to receive prompt treatment for the best outcome.

How is a breast abscess treated?

Your gynaecologist will first need to examine the lump. If an abscess has been diagnosed, you will be given an urgent referral to a surgeon to confirm the diagnosis and for treatment. An ultrasound scan can confirm a diagnosis of an abscess as well as determine if there is more than one pocket of pus.

The abscess will need to be drained to remove the fluid (pus) from the breast. If the abscess is small, a needle and syringe will be used to drain away the fluid. However a small incision or cut will be necessary to drain away the fluid if the abscess is large. Regardless of how the fluid is drained, you will first be given a local anaesthetic to numb the skin around the abscess and an ultrasound may be used to help guide the medical instrument used for draining the pus.

The pus will then be cultured (artificially grown) to determine the type of antibiotic that should be prescribed.

Prompt, appropriate treatment can lead to a full recovery. Delayed treatment can result in complications that include problems with breastfeeding in the future, sepsis (bacterial blood infection), scarring and chronic pain.

Is it fine to breastfeed while being treated for a breast abscess?

Based on guidelines from the World Health Organisation (WHO) and the National Institute for Health and Care Excellence (NICE), you should continue to breastfeed from both breasts. This is because studies have shown that even with an infection it is safe for the baby to continue breastfeeding from the affected breast, and emptying the breast is important in treating the condition. However, some babies may notice a difference in the milk and refuse to feed from the affected breast - you can try offering that breast first during a feed. If your baby won't take milk from the affected breast or it is too painful, you will need to use a breast pump to express milk until the breast is empty.