If a mouth ulcer occurs during breastfeeding, you can first apply mouthwash to remove the bacteria on the surface of the mouth ulcer or the necrotic tissue on the surface of the mouth ulcer, and you can also apply ulcer patches or apply vitamin C for topical application. In most cases, the mouth ulcer surface can heal itself under the effect of vitamin C. In addition, there are also drugs that can be used, such as recurrent aphthous ulcers, which should be treated mainly locally, such as spraying some epidermal growth factor gel to promote the healing of the ulcer. Usually, such topical medications do not have any adverse effects on lactating women and milk production, but more importantly, the main reason for the mouth ulcers is the reduced vitamin intake in the diet. Therefore, during the breastfeeding period, you should pay more attention to ensure balanced nutrition, eat more fruits and vegetables in moderation, keep your bowels open, and chew slowly when eating to avoid biting the local oral mucosa, which can reduce the recurrence of mouth ulcers.