External irritation or injuries commonly cause canker sores and other mouth blisters. Accidentally biting your lips, as well as allergies, dental work, and certain toothpastes and mouthwashes, can lead to canker sores.

 

A common cause of cold sores and other blisters outside and inside of the mouth is the herpes simplex virus. This infection can spread through kissing, oral sex, or sharing eating utensils and other objects that touch the mouth. Herpes usually isn’t serious, but it can cause complications for people with weakened immune systems from medication or pre-existing illnesses. 

 

Infections and viruses can also lead to thrush. The fungus that causes thrush, Candida, naturally lives in our mouths in small amounts. Our immune system is meant to keep this fungus under control. However, in older adults, very young children, and others with reduced immunity, the fungus can overrun the mouth and create a thrush rash.

 

Early symptoms of mouth cancer include sores and other unusual marks or rashes inside the mouth. A sign of mouth cancer is bright red, white, or grey patches on the cheeks, under the tongue, and behind the back teeth. Generally, cancerous sores last beyond two weeks, unlike most canker sores and other mouth blisters.

 

 

If your mouth blisters do not resolve on their own within a few weeks or recur even with over-the-counter treatments, contact your doctor. The blisters could be a symptom of an underlying condition that needs attention.