A fungal infection, also called a yeast infection or thrush, can form on your nipples or in your breast. This type of infection thrives on milk and forms from an overgrowth of the Candida organism. Candida lives in our bodies and is kept healthy by the natural bacteria in our bodies. When the natural balance of bacteria is upset, Candida can overgrow, causing an infection.

A key sign of a fungal infection is sore nipples that last more than a few days, even after your baby has a good latch. Or you may suddenly get sore nipples after several weeks of pain-free breastfeeding. Other signs are pink, flaky, shiny, itchy, or cracked nipples or deep pink and blistered nipples. You also could have achy breasts or shooting pains deep in the breast during or after feedings.

Causes of fungal infection include:

• Thrush in your baby's mouth, which can pass to you
• An overly moist environment on your skin or nipples that are sore or cracked
• Use of antibiotics or steroids, perhaps during labor
• A chronic illness like HIV, diabetes, or anemia

What you can do

Fungal infections may take several weeks to clear up, so it is important to follow these tips to avoid spreading the infection:

• Change disposable nursing pads often.
• Wash any towels or clothing that comes in contact with the yeast in very hot water (above 122°F).
• Wear a clean bra every day.
• Wash your hands often.
• Wash your baby's hands often, especially if he or she sucks on his or her fingers.
• Boil every day all pacifiers, bottle nipples, or toys your baby puts in his or her mouth. (To boil them, place them in a pot of water and heat the water to a rolling boil.)
• After one week of treatment, throw away all pacifiers and nipples and buy new ones.
• Boil every day all breast pump parts that touch your milk.
• Make sure other family members are free of thrush or other fungal infections. If they have symptoms, make sure they get treated.

source: http://www.womenshealth.gov