The symptoms of mastitis most often appear within 4 to 6 weeks after childbirth.

If you have mastitis, you may first notice:

• A painful area on one breast. It may be reddened, warm to the touch, or both.
• Chills, aches, and flu-like symptoms.
• A temperature of 100F or higher.

These initial symptoms may start after you have resolved a blocked milk duct.

Worsening symptoms

As a mastitis infection gets worse, you may notice:

• An increased heart rate (more than 100 beats per minute).
• Thick, yellow drainage (pus) coming from the nipple.
• Swollen and tender lymph nodes in your armpit on the same side as the infected breast.

Breast abscess

Occasionally symptoms of mastitis get worse and the breast develops a pocket of pus (abscess) in the infected area. Symptoms of a breast abscess include:

• A breast lump that is hard and painful.
• A reddened area on the breast.
• Flu-like symptoms that are getting worse.

Thrush infection

Thrush (yeast infection) can occur in your baby's mouth and spread to your nipples and breast ducts. If you have symptoms of mastitis that are not going away in spite of treatment, pain in the nipple area during and after breast-feeding, sharp breast pain in between feedings, or nipples that look very pink, you may have thrush. This condition can also begin with a sudden start of pain or burning when breast-feeding has been going well without problems.

If you have thrush symptoms, both your nipples and your baby's mouth should be checked for thrush. Treatment for thrush requires that both you and your baby be treated, even if your baby doesn't have symptoms. For more information, see the topic Thrush.