OBJECTIVE: To document skin changes in the nipple during the 1st week of breastfeeding and to explore the relationship of such changes to pain. DESIGN: Longitudinal descriptive study. Subjects were visited four times during the 1st week of breastfeeding. SAMPLE: Convenience sample of 20 Caucasian women. SETTING: Hospital and home. MAIN OUTCOME MEASURES: Observed skin characteristics of the nipple included erythema, edema, fissures, blisters, inflamed areas, eschar, white patches, dark patches, yellow patches, peeling, pus, and ecchymosis. Subject-rated nipple pain. RESULTS: Skin changes were identified and quantified. Changes were visible in 100% (20) of the sample, and 65% (13) had severe skin damage; 90% (18) of the subjects reported pain. Some correlations between skin characteristics and pain were statistically significant, but not clinically meaningful. Skin damage was concentrated on the tip of the nipple. CONCLUSIONS: The data chronicle skin changes and their relationship to nipple pain during the 1st week of breastfeeding. Normal neonatal sucking appears to induce a suction wound on the skin of the nipples of many breastfeeding women that may account for pain experienced at the onset of lactation.