If you're like 20 percent of the population, you've experienced white, painful ulcer/lesions on the inside of your lips and gums before. These ulcerations are called canker sores (medically as aphthous ulcers), and are often mistaken for cold sores. But unlike cold sores, these aren't caused by the herpes virus, and they aren't contagious.
Causes of canker sores are varied and there's no definitive explanation of what triggers the appearance of these painful ulcers. However, researchers have linked several factors, including minor injuries to the mouth area, food allergies, bacterial allergies, hormones, and stress.
Though painful and uncomfortable, canker sores don't typically warrant treatment, as they usually go away in a week or two. Topical pain relievers such as benzocaine and oral antiseptics like hydrogen peroxide may relieve pain and speed up the healing process.