During breastfeeding, hormones are released to create milk flow.
Prolactin causes your alveoli (part of the lungs) to take protein and sugar from the blood and turn them into breast milk. Then, oxytocin is released, causing the cells around the alveoli to contract and force the breast milk towards the milk ducts in the mammary gland.
When milk supply gets trapped in the milk ducts and cannot be released, mastitis occurs.
Other causes of mastitis
A bacterial infection. During breastfeeding, bacteria from your skin and baby’s mouth can enter the duct through the opening or cracked nipple skin. Stagnant milk in the affected breast (“milk stasis”) becomes a breeding ground for bacteria.
Bacterial infections can also occur in those who are not breastfeeding, specifically after menopause. The ducts below the nipple can become inflamed or clogged with dead skin cells and debris due to hormonal changes. For those not breastfeeding, this is known as chronic/acute mastitis or periductal mastitis.
A clogged milk duct. Sometimes the breast doesn’t completely empty after breastfeeding, causing a build up of breast milk. The clogged duct causes milk to back up, leading to a breast infection.
Nipple damage. If the nipple is cracked or damaged, it makes it easier for harmful bacteria to enter the breast and cause infectious mastitis.
Yeast infection. Secondary infections such as thrush (yeast infection) can cause inflammation and a blocked milk duct and mastitis.