NCBI Medgen - Cracked nipple in pregnancy, the puerperium or lactation (https://www.ncbi.nlm.nih.gov/medgen/578331)
[2]
PMC NCBI - Prevalence and factors associated with cracked nipples in the first weeks of breastfeeding (https://pmc.ncbi.nlm.nih.gov/articles/PMC4975913/)