Causes
Since the 1980s mastitis has often been divided into non-infectious and infectious sub-groups. However, recent research suggests that it may not be feasible to make divisions in this way. It has been shown that types and amounts of potentially pathogenic bacteria in breast milk are not correlated to the severity of symptoms. Moreover, although only 15% of women with mastitis in Kvist et al.'s study were given antibiotics, all recovered and few had recurring symptoms. Many healthy breastfeeding women wishing to donate breast milk have potentially pathogenic bacteria in their milk but have no symptoms of mastitis.
Mastitis typically develops when the milk is not properly removed from the breast. Milk stasis can lead to the milk ducts in the breasts becoming blocked, as the breast milk not being properly and regularly expressed. It has also been suggested that blocked milk ducts can occur as a result of pressure on the breast, such as tight-fitting clothing or an over-restrictive bra, although there is sparse evidence for this supposition . Mastitis may occur when the baby is not appropriately attached to the breast while feeding, when the baby has infrequent feeds or has problems suckling the milk out of the breast.
Experts are still unsure why breast milk can cause the breast tissue to become inflamed. One theory is that it may be due to the presence of cytokines in breast milk. Cytokines are special proteins that are used by the immune system and are passed on to the baby in order to help them resist infection. It may be the case that the woman's immune system mistakes these cytokines for a bacterial or viral infection and responds by inflaming the breast tissue in an attempt to stop the spread of what the body perceives as an infection.
Some women (approximately 15% in Kvist et al. study) will require antibiotic treatment for infection which is usually caused by bacteria from the skin or the baby's mouth that entering the milk ducts through skin lesions of the nipple or through the opening of the nipple. Infection is usually caused by staphylococcus aureus.
Mastitis is quite common among breastfeeding women. The WHO estimates that although incidences vary between 2.6% and 33%, the prevalence globally is approximately 10% of breastfeeding women. Most mothers who develop mastitis usually do so within the first few weeks after delivery. Most breast infections occur within the first or second month after delivery or at the time of weaning. However, in rare cases it affects women who are not breastfeeding.
Mastitis can also develop after nipple piercing. In some rare cases Mastitis can also occur in men.
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