A mouth ulcer is a sore that appears anywhere inside your mouth. These sores are usually red, yellow or white, and you might have one or several.

You can get mouth ulcers on your:

Gums
Tongue
Roof of mouth (palate)
Inner cheeks
Inner lips

These sores are often painful and can make eating, drinking and speaking uncomfortable.

Mouth ulcers can be alarming. However, they’re not a sexually transmitted infection (STI) and you can’t get or spread them from kissing or sharing food and drinks. Aside from any pain and discomfort, mouth ulcers are usually harmless and go away on their own in a week or two. But some types of mouth sores could point to underlying health conditions like viruses, autoimmune diseases or gastrointestinal issues.

Types of mouth ulcers

There are many different types of mouth sores and lesions, including:

Canker sores (aphthous ulcers)
These are the most common type of mouth ulcers. Healthcare providers aren’t exactly sure what causes them or why some people get them more than others do. Causes include minor trauma (like biting your cheek), acidic foods and even stress. Canker sores are usually white or yellow with red around the edges.

Oral lichen planus
This condition can cause itchy rashes and lacelike, white sores inside your mouth. Oral lichen planus is an immune system response and most commonly affects women and people assigned female at birth (AFAB) age 50 or older.

Leukoplakia
This condition causes white or gray patches inside your mouth. It develops because of excess cell growth. Chronic irritation from things like smoking or chewing tobacco can cause it. But sometimes it happens for no apparent reason. Leukoplakia lesions usually aren’t cancerous.

Erythroplakia
Erythroplakia is another symptom of smoking or chewing tobacco. People with erythroplakia have red patches that commonly appear behind their lower front teeth or under their tongue. Unlike leukoplakia lesions, erythroplakia patches are usually precancerous or cancerous.
 
Oral thrush
An overgrowth of yeast called Candida albicans causes this fungal infection inside your mouth. It commonly happens after antibiotic treatment or when your immune system isn’t as strong as it usually is. Oral thrush causes red and creamy white mouth sores and patches.
 
Mouth cancer
Oral cancer lesions can show up as red or white mouth sores or ulcers. These sores won’t heal on their own. If you have a mouth ulcer that hasn’t gone away after three weeks, tell your healthcare provider.

Symptoms and Causes
 
What are the symptoms of a mouth ulcer?
 
Mouth ulcers are usually easy to spot. They appear as sores on your gums, tongue, inner cheeks, inner lips or roof of your mouth.

Mouth sores are typically:

Red around the edges.
White, yellow or gray in the center.

You may only develop one ulcer, or there might be more. Other symptoms could include:

Swelling around the ulcers.
Increased soreness when brushing your teeth.
Pain that worsens when eating spicy, salty or sour foods.

What causes mouth ulcers?

Mouth ulcers may occur for a number of reasons, including:

Minor tissue injury from dental work, such as having a cavity filled.
Accidentally biting your cheek or tongue.
An allergic reaction to certain bacteria.
Wearing braces or retainers.
Using harsh or abrasive toothpaste.
Eating lots of acidic foods, such as oranges, pineapples and strawberries.
Hormonal changes during your period.
Stress.
Lack of sleep.

Health conditions associated with mouth ulcers

Certain health conditions, including many autoimmune diseases, can also cause mouth ulcers. These conditions may include:

Vitamin deficiencies.
Viral, bacterial or fungal infections.
Crohn’s disease.
Celiac disease.
Reactive arthritis.
Lupus.
Behçet’s disease.

Are mouth ulcers contagious?

No. Unlike cold sores, mouth ulcers aren’t contagious, and they can’t spread through kissing or sharing food.

Cold sores (fever blisters) appear on the outside of your mouth, often on your lips. A virus causes them, and they’re very contagious. If you have a fever blister, you should avoid sharing personal items with other people to reduce the spreading of the virus.

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