Canker sores and oral cancer lesions may seem similar but there are ways to tell the difference. A lesion that's red, typically flat, and painful early on is usually a canker sore (aphthous ulcer).

Causes of a sore throat on one side includes the flu, tonsillitis, a canker sore, or a tumor. Look out for other symptoms to help you identify what's causing your sore throat on one side.