Prophylactic peppermint gel (along with appropriate breastfeeding education and support) may help prevent cracked nipples. Peppermint has a number of qualities that bode well for its use on the nipples of breastfeeding mothers. It can have a calming and numbing effect on irritated skin, increases tissue flexibility which in turn increases resistance to cracking, is antibacterial, anti-inflammatory, and is an antioxidant that demonstrates fungicidal qualities. Prophylactic use of a peppermint gel preparation has been shown to reduce nipple cracks over the first few weeks of breastfeeding.
Melli, M.S., Rashidi, M.R., Nokhoodchi, A., Tagayi, S., Sadaghat, K., Tahmasebi, Z., & Sheshvan, M.K. (2007) A randomized trial of peppermint gel, lanolin ointment, and placebo gel to prevent nipple crack in primiparous breastfeeding women.  Medical Science Monitor, 13(9): CR 406-411.