Objectives: To identify potential risk factors for the development of mastitis in breastfeeding women.

Methods: A prospective cohort study with questionnaire and telephone follow-up was conducted. Women were recruited after delivery at either the teaching hospital or the only private hospital with an obstetric service during May to December 1994 in Newcastle, New South Wales and were followed up at home for six months. 1,075 breastfeeding women were recruited and were sent follow-up questionnaires at three, eight and 26 weeks post-delivery.

Results: Mastitis occurred in 20% (95% CI 18-22%) of women during the first six months. Factors that were statistically significantly and independently related to mastitis were: past history of mastitis (adjusted Hazard Ratio=1.74, 1.07-2.81), university or college education (HR=1.93, 1.18-3.16), blocked duct (HR=2.43, 1.68-3.49), cracked nipples (HR=1.44, 1.00-2.07), use of creams on nipples (HR=1.83, 1.22-2.73), particularly papaya cream (Relative Risk = 1.83, 1.36-2.47), and always starting with the alternate breast on consecutive feeds (HR=2.28, 1.50-3.44).

Conclusions: Women with a past history of mastitis had an increased risk of developing mastitis. Blocked ducts and cracked nipples serve as warning signs for mastitis. Use of some creams may increase the risk of mastitis and their value should be tested in clinical trials.

Implications: We have identified several pre-natal and post-natal markers for increased risk of mastitis that may assist in its early identification and treatment. The use of creams on nipples may introduce pathogens that cause mastitis and should be avoided.