Blister on the inside of my mouth and if I smile or grin it hurts a little. Is it a cold sore or canker sore?

Your Dentist Knows. Cold sores (herpes simplex 1) are usually red and on the surrounding tissues of the mouth. Canker sores (aplthous ulcers) are generally white and on thesoft tissue inside the mouth. Your dentist is trained to tell the difference. Both are made worse by stress & will recur. Herpes is a virus, aphthous is believed to be autoimmune in nature. See your dentist to be sure you know what you have.