Mastitis is when your breast becomes red, hot and painful.
It's most common in breastfeeding women, but women who are not breastfeeding and men can also get it.
Mastitis usually only affects 1 breast, and symptoms often come on quickly. They include:
You may also get flu-like symptoms, such as aches, a high temperature, chills and tiredness.
A GP will usually prescribe antibiotics.
If you're breastfeeding a very small amount of the antibiotic may go into your breast milk. There is no risk to your baby, but it might make them irritable and restless.
If you are breastfeeding and keep getting mastitis, it might be due to problems with positioning and attaching.
If you have any breastfeeding problems, it's important to ask for help from a midwife, health visitor or a breastfeeding specialist as soon as possible.
You can also call the National Breastfeeding Helpline on 0300 100 0212 (9.30am to 9.30pm, daily)
Mastitis is common in breastfeeding women as it can be caused by a build-up of milk.
Women who are not breastfeeding can also get mastitis, as can men. This can happen due to: