What does a minor canker sore look like?

Depends on cause: A herpes lesion starts out as a painful blister then turns into a shallow white to yellow ulcer if it is in the mouth or scab if it is on the lip. An aphthous ulcer is on the cheek, soft palate, tongue and is a shallow ulcer with a red rim. Yeast infections in the mouth look like white dot pasted on the lining with a red margin. Syphilis looks like a moist scab.

White ulceration: Whitish or pinkish ulceration surrounded by a red halo of tissue.