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Mastitis is a painful condition of the breast, which becomes red, hot and sore (inflamed). Sometimes it becomes infected. Mastitis is common in breast-feeding women. It is usually treated with a course of antibiotics. It is best to try to continue to breast-feed if you have mastitis. Breast-feeding when you have mastitis will not harm your baby.

Cross-section diagram of a breast

Mastitis is an inflammation of the breast, usually caused by a build-up of milk within the breast in mothers who are breast-feeding. It can be either:

  • Non-infectious - when the build-up of milk provokes a reaction in the breast tissue, causing it to become red, hot and swollen (inflamed).
  • Infectious - when the breast tissue becomes infected as a result of the milk which has built up within it. The infection is caused by germs (bacteria) which may have come from the skin.

If non-infectious mastitis is not treated, it can develop infection, and become infectious mastitis. You can't tell which type of mastitis it is from looking at it, and the treatment is the same.

Anything which causes a build-up of milk in your breasts will make it more likely that you develop mastitis. Sometimes it occurs if you suddenly stop breast-feeding and the breasts become very swollen and sore because of the milk. This might happen if your baby starts to sleep through the night, or if you start using bottles for some feeds. If your baby is not feeding very well (for example, due to tongue-tie, or abnormalities of the lips, or illness) this might cause the milk to collect. Pressure on the breast due to a tight bra, or sleeping on your front, or wearing a seatbelt for a long time, may also be a cause. Breaks in the skin of the breast, such as cracked nipples, can make mastitis more likely. This is because the germs on the skin then have a route to the inside of the breast.

Mastitis occurs most often in breast-feeding mothers. It typically develops within the first few weeks of breast-feeding. 1 in 10, and possibly as many as 3 in 10 breast-feeding mothers get mastitis.

Mastitis sometimes occurs in women who are not breast-feeding. Germs (bacteria) get into the milk ducts of the breast to cause the infection. This may be through a crack or sore in the nipple or from a nipple piercing. Some women without sore nipples also develop mastitis.

Mastitis causes an area of hardness, pain, redness and swelling in the breast. It often starts in a wedge-shaped section of breast. It usually occurs in one breast only.

You may also develop a high temperature and feel unwell, with flu-like symptoms. These might include muscle pains, headaches, and feeling tired and low.

A blocked milk duct sometimes occurs in breast-feeding women. A blocked milk duct also causes a painful, swollen area in a breast. The overlying skin is sometimes red and inflamed, but it tends to be not as bad as mastitis caused by an infection.

When you feed your baby, the pain may increase due to the pressure of milk building up behind the blocked duct. A blocked milk duct will usually clear within 1-2 days and symptoms will then go. However, in some cases a blocked milk duct becomes infected and develops into mastitis. So, some cases of mastitis develop as a complication of a blocked milk duct, but some cases occur without a preceding blockage.

A blocked milk duct may clear more quickly by feeding your baby more often from the affected breast and gently massaging your breast whilst feeding.

Mastitis is usually treated with a course of an antibiotic. However, a mild case may get better without any treatment. If you notice a tender swollen area in a breast when you are breast-feeding, it may be a blocked milk duct or a developing mastitis. It may be reasonable to 'see how it goes' over a day or so.

The following measures may help to treat your mastitis without the need for antibiotics:

  • Continue to breast-feed. This will empty the affected breast, and keeps the milk flowing.
  • Feed on the affected side first, so it will empty well, for the next two or three feeds. (However, don't let the unaffected side become too full of milk.)
  • After feeding, consider expressing from the affected side as well. This is to make sure the breast is emptied.
  • Before feeding, massage your breast gently. Or apply heat with a warm flannel, heat pack or by having a warm shower.
  • Ask your midwife or health visitor to check your breast-feeding technique, and to check that your baby is latching on well.
  • If it is too painful to feed from the affected side, express the milk from that side with a breast pump.
  • Try to eat well and drink plenty of fluid.

However, if your symptoms become worse you should see a doctor. After talking to you and examining you, they may prescribe an antibiotic. The infection will usually clear within a few days of starting the antibiotic.

Occasionally, an abscess may form inside an infected section of breast. An abscess is a collection of pus that causes a firm, red, tender lump. This is thought to happen in 3 to 7 in every 100 cases of mastitis. The pus can be seen with an ultrasound scan. If the skin over the abscess is not broken, the pus can be drained with a needle and syringe by a doctor. If the skin is broken (or very thin) the doctor may need to make a small cut to let the pus drain out.

  • If you are breast-feeding, continue to feed from the affected breast. This helps the milk to continue flowing and stops the breast from becoming engorged and making things worse.
  • Feeding from an infected breast does not harm the baby. If the baby swallows bacteria from an infected breast, the germs (bacteria) will be killed by the acid in the baby's stomach.
  • The doctor will choose an antibiotic that is safe to give to breast-feeding women and which will not harm the baby.
  • You can take simple painkillers (such as paracetamol or ibuprofen) to ease pain and reduce high temperature (fever). Cold packs can also be quite soothing when placed on the breast.
  • A breast-feeding baby may refuse to feed from the affected breast, as the taste of the milk may change a little. If this occurs, feed from the other breast. Do remember to express the milk (that your baby has refused to take) from the affected breast. This will stop the breast swelling and becoming more painful. It will also keep up the demand for milk, so production does not slow down.
Original Author:
Dr Tim Kenny
Current Version:
Peer Reviewer:
Dr Hannah Gronow
Document ID:
4840 (v40)
Last Checked:
Next Review:
The Information Standard - certified member
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