It is not recommended to put vitamin C on the wound of a mouth ulcer because vitamin C can release acids that irritate the wound and aggravate the pain of the wound. Ulcers are not associated with vitamin C deficiency, so even putting vitamin C on the wound does not treat the ulcer. In the case of recurrent aphthous ulcers, you can put a film on the ulcer wound, for example, there is a film with sodium carboxymethylcellulose, with gentamycin and anesthetics in it, which can be applied to the wound to reduce inflammation and pain. You can also put tretinoin ointment on the wound, or put ice borax, watermelon cream, iodized glycerin, etc. on the wound, all of which can help reduce inflammation and pain, and promote healing. If it is a traumatic ulcer, putting vitamin C is even more ineffective, need to find out whether there is a sharp tooth tip or marginal ridge in the neighborhood, and make the tooth tip or marginal ridge become rounded by adjusting and grinding, only remove the irritating factors, the wound can heal as soon as possible.