Mastitis is a condition that causes inflammation and pain in the breast and usually occurs when a women is breastfeeding.

The condition is caused by a build-up of milk accumulating in the breast, which is referred to as milk stasis. In some cases, this milk can become infected, in which case the term infective mastitis applies. Mastitis can also develop in women who do not breastfeed, and this is usually caused by injury or damage to the nipple due to a piercing or wound, for example.

Causes of mastitis

Milk stasis can develop when the breast is not completely emptied of milk at the end of breastfeeding sessions. This can occur if the baby’s mouth is not properly attaching to the breast during feeding or if feeding sessions are missed or infrequent. Milk stasis can also develop in cases where women favour one breast for feeding because the other nipple is sore or injured, for example.

Other causes of milk stasis include wearing tight-fitting clothing or seat belts and sleeping front side down. A knock or injury to the breast can also damage the milk ducts, impairing milk flow and leading to milk stasis.

Mastitis may also occur in women who do not breastfeed. An injury or crack in the nipple caused by a wound or piercing can expose the breast to infection with bacteria. This form of mastitis is known of as periductal mastitis and usually occurs in women aged 20 to 35 years. The condition is also more common among smokers than nonsmokers.

A rare condition called duct ecstasia is another cause of mastitis among women who are not breastfeeding. This is caused by the milk ducts becoming shorter and wider as a woman ages and approaches her menopause. The condition is usually harmless but can sometimes cause a thick secretion to accumulate in the ducts, which can cause irritation and inflammation.