In breastfeeding women, mastitis is often caused by a build-up of milk within the breast – known as milk stasis. In some cases, this build-up of milk can also become infected.

In non-breastfeeding women, mastitis most often occurs when the breast becomes infected as a result of damage to the nipple.

Mastitis in breastfeeding women

Milk stasis

Many cases of mastitis in breastfeeding women are thought to be caused by milk stasis. This occurs when the milk is not properly removed from your breast during breastfeeding. It can be caused by:

• a baby not properly attaching to the breast during feeding – this may mean that not enough milk is removed (see breastfeeding position and attachment for advice on helping your child feed correctly)
• a baby having problems sucking – for example, because they have a tongue-tie (a piece of skin between the underside of their tongue and the floor of their mouth)
• infrequent or missed feeds – for example, when they start to sleep through the night
• favouring one breast for breastfeeding – for example, because one of your nipples is sore; this can lead to milk stasis developing in the other breast
• a knock or blow to the breast that damages the milk duct or the glands in your breast
• pressure on your breast – for example, from tight-fitting clothing (including bras), seat belts or sleeping on your front

Milk stasis can cause the milk ducts in your breasts to become blocked, and can cause milk to build-up within the affected breast.

Experts are not sure exactly why breast milk can cause the breast tissue to become inflamed. One theory is that the pressure building up inside the breast forces some milk into the surrounding tissue.

Your immune system may then mistake proteins in the milk for a bacterial or viral infection and responds by inflaming the breast tissue, in an effort to stop the spread of infection.

Infection

Fresh human milk does not usually provide a good environment in which bacteria can breed. However, milk stasis can cause milk to stagnate and become infected. This is known as infective mastitis.

Exactly how bacteria enter the breast tissue has not been conclusively proven. It may be that the bacteria that usually live harmlessly on the skin of your breast enter through a small crack or break in your skin, or that bacteria present in the baby’s mouth and throat are transferred during breastfeeding.

You may be at greater risk of developing infective mastitis if your nipple is damaged – for example, as a result of using a manual breast pump incorrectly or your baby having a cleft lip or palate (an opening or split in their lip or roof of their mouth).

Mastitis in breastfeeding women is more likely to be caused by an infection if self-help measures to express milk from the affected breast have not improved symptoms within 12-24 hours. Read more about treating mastitis.

Mastitis in non-breastfeeding women

In women who don’t breastfeed, mastitis is often caused by a bacterial infection. This can occur as a result of bacteria getting into the milk ducts through a cracked or sore nipple, or a nipple piercing.

This type of mastitis is known as periductal mastitis. It usually affects women who are in their late 20s and early 30s, and is more common among women who smoke.

Occasionally, mastitis can occur in non-breastfeeding women as a result of duct ectasia. This is when the milk ducts behind the nipple get shorter and wider as the breasts age. It typically occurs in women approaching the menopause.

Duct ectasia is usually nothing to be concerned about, but in some cases a thick, sticky secretion can collect in the widened ducts, and this can irritate and inflame the duct lining.

Mastitis is a condition that causes a woman’s breast tissue to become painful and inflamed. It can usually be treated easily, but it’s important to see your GP if you think you have it.

Mastitis is most common in breastfeeding women. Up to 1 in every 10 women who breastfeed are affected, usually within the first three months after giving birth.

Mastitis related to breastfeeding is sometimes called lactation mastitis or puerperal mastitis by doctors.

However, women who aren’t breastfeeding can also develop mastitis. Non-breastfeeding women often have a type called periductal mastitis.

What causes mastitis?

In breastfeeding women, mastitis is often caused by a build-up of milk within the breast. This is known as milk stasis.

Milk stasis can occur for a number of reasons, including:

• a baby not properly attaching to the breast during feeding
• a baby having problems sucking
• infrequent feeds or missing feeds

In some cases, this build-up of milk can also become infected with bacteria. This is known as infective mastitis.

In non-breastfeeding women, mastitis most often occurs when the breast becomes infected as a result of damage to the nipple, such as a cracked or sore nipple, or a nipple piercing.

Read more about the causes of mastitis.

Symptoms of mastitis

Mastitis usually only affects one breast, and symptoms often develop quickly.

Symptoms of mastitis can include:

• a red, swollen area on your breast that may feel hot and painful to touch
• a breast lump or area of hardness on your breast
• a burning pain in your breast that may be continuous, or may only occur when you are breastfeeding
• nipple discharge, which may be white or contain streaks of blood

You may also experience flu-like symptoms, such as aches, a high temperature (fever), chills and tiredness.

When to seek medical advice

You should contact your GP as soon as possible if you think you might have mastitis. Before your appointment it may help to try some self-help measures (see below).

It’s important to see your GP promptly because there is a risk that mastitis could lead to a breast abscess (a painful collection of pus), which may need to be drained surgically.

Breast abscesses can be serious if not spotted or treated quickly; it’s estimated that 1 in every 10 women who develop them are unable to breastfeed using the affected breast again.

Diagnosing mastitis

Your GP will often be able to diagnose mastitis based on your symptoms and an examination of your breasts.

If you’re breastfeeding, they may ask you to demonstrate your technique. Try not to feel as if you are being tested or blamed – breastfeeding correctly can take time and practice.

If your symptoms are particularly severe, you have had recurrent episodes of mastitis, or you have been given antibiotics and your condition hasn’t improved, your GP may decide to take a small sample of your breast milk for testing.

This will help determine whether you have a bacterial infection and can identify the specific type of bacteria responsible for your condition. Knowing which bacteria are causing the infection will allow your GP to prescribe an antibiotic that is specifically effective against those bacteria.

If you have mastitis and are not breastfeeding, your GP may refer you to hospital for a specialist examination and a breast scan to rule out other conditions, particularly if your symptoms haven’t improved after a few days of treatment. Scans you may have include an ultrasound scan or a mammogram (X-ray of the breast).

How mastitis is treated

Mastitis can usually be easily treated and most women will make a full recovery very quickly.

Self-help measures are often helpful, such as:

• getting plenty of rest and staying well hydrated
• using over-the-counter painkillers, such as paracetamol or ibuprofen, to reduce any pain or fever
• avoiding tight-fitting clothing (including bras) until your symptoms improve
• if you are breastfeeding, continuing to feed your baby and making sure your baby is properly attached to your breast

Breastfeeding your baby when you have mastitis, even if you have an infection, will not harm your baby and can help improve your symptoms. It may also help to feed more frequently than usual, express any remaining milk after a feed and express milk between feeds.

For non-breastfeeding women with mastitis, and breastfeeding women with a suspected infection, a course of antibiotic tablets will usually be prescribed to bring the infection under control.

Read more about treating mastitis.

Preventing mastitis

Although mastitis can usually be treated easily, the condition can recur if the underlying cause is not addressed.

If you are breastfeeding, you can help reduce your risk of developing mastitis by taking steps to stop milk building up in your breasts, such as:

• breastfeed exclusively for around six months, if possible
• encourage your baby to feed frequently, particularly when your breasts feel overfull
• ensure your baby is well attached to your breast during feeds – ask for advice if you are unsure (see below)
• let your baby finish their feeds – most babies will release the breast when they have finished feeding; try not to take your baby off the breast unless they are finished
• avoid suddenly going longer between feeds – if possible, cut down gradually
• avoid pressure on your breasts from tight clothing, including bras

Your GP, midwife or health visitor can advise about how to improve your breastfeeding technique. You can also call the National Breastfeeding Helpline on 0300 100 0212 for advice.

The Map of Medicine is used by doctors throughout the NHS to determine the best treatment options for their patients. NHS Choices offers everyone in England exclusive and free access to this cutting-edge internet resource, which lets you see exactly what your doctor sees.

The information in the Map has been approved by the UK’s leading clinical experts, is based on the best available clinical evidence, and is continually updated. To take advantage of this unique resource go to:

Map of Medicine: mastitis

Mastitis can usually be easily treated, and most women will make a full recovery very quickly.

Many cases of mastitis not caused by an infection will improve through using self care techniques, such as:

• making sure you get plenty of rest
• drinking plenty of fluids
• using over-the-counter painkillers such as paracetamol or ibuprofen to reduce any pain or fever – a small amount of paracetamol can enter the breast milk, but it is not enough to harm your baby (it is not safe to take aspirin while breastfeeding)
• avoiding tight-fitting clothing (including bras) until your symptoms improve
• if you are breastfeeding, regularly expressing milk from your breasts (see below)
• placing a warm compress (a cloth soaked with warm water) over your breast to help relieve the pain – a warm shower or bath may also help

If your GP thinks your mastitis is caused by an infection, you may need to take antibiotics. 

Expressing breast milk

If you are breastfeeding and you have mastitis, it is likely to be caused by a build-up of milk within the affected breast. Regularly expressing milk for your breast can often help improve the condition quickly.

One of the best ways to express milk from your breast is to continue breastfeeding your baby, or expressing milk by hand or by using a pump. Continuing to breastfeed your baby will not harm them, even if your breast is also infected.

The milk from the affected breast may be a little saltier than normal, but it is safe for your baby to drink. Any bacteria present in the milk will be harmlessly absorbed by the baby’s digestive system and will not cause any problems.

You may find that expressing breast milk becomes easier by:

• breastfeeding your baby as often and as long as they are willing to feed, starting feeds with the sore breast first
• making sure your baby is properly positioned and attached to your breasts – your midwife or health visitor will advise you about how to do this (read more about breastfeeding positioning and attachment)
• experimenting by feeding your baby in different positions
• massaging your breast to clear any blockages – stroke from the lumpy or tender area towards your nipple to help the milk flow
• warming your breast with warm water, as this can soften it and help your breast milk flow better, making it easier for your baby to feed
• making sure that your breast is empty after feeds by expressing any remaining milk
• if necessary, expressing milk between feeds (see expressing breast milk for more information) 

Contact your GP if your symptoms worsen or do not improve within 12-24 hours of trying these techniques. If this happens, it is likely that you have an infection and will need antibiotic medication.

Antibiotics

If you are breastfeeding and the above measures have not helped improve your symptoms, or if your GP can see your nipple is clearly infected, you will be prescribed a course of antibiotics to kill the bacteria responsible. These should be taken in addition to continuing the self-help measures above.

Your GP will also usually prescribe a course of antibiotics if you develop mastitis and are not breastfeeding.

If you are breastfeeding, your GP will prescribe an antibiotic that is safe to use. This will usually be a tablet or capsule that you take orally (by mouth) four times a day for up to 14 days.

A very small amount of the antibiotic may enter your breast milk, which may make your baby irritable and restless, and their stools may become looser (runnier) and more frequent. This is usually temporary and will resolve once you have finished the course of antibiotics. They do not pose a risk to your baby.

Contact your GP again if your symptoms worsen or have not begun to improve within 48 hours of starting antibiotic treatment.

Surgery

In some cases of mastitis in non-breastfeeding women that recur frequently or persist despite treatment, surgery to remove one or more of your milk ducts may be recommended.

This operation is usually performed with a general anaesthetic (where you are asleep) and lasts about 30 minutes. Most people can go home the same day as the procedure, or the day after.

If all of the milk ducts in one of your breasts are removed during this operation, you will no longer be able to breastfeed using that breast. You may also lose some sensation in the nipple of the treated breast(s). Make sure you discuss all the risks and implications of surgery with your doctor and surgeon beforehand.