Mouth sores are painful or irritated spots that develop on the soft tissues inside your mouth, including the gums, inner cheeks, tongue, lips, and the floor or roof of the mouth. They affect between 5 and 25% of the general population at any given time, with some studies estimating rates as high as 60% depending on the group studied. Most are harmless and heal on their own within two weeks, but they can make eating, drinking, and talking uncomfortable in the meantime.
Common Types of Mouth Sores
Not all mouth sores are the same. The type you’re dealing with determines what caused it and how to treat it.
Canker sores (aphthous ulcers) are the most common type. They appear as small, round or oval sores with a white or yellowish center and a red border. They form inside the mouth and are not contagious. They tend to peak in frequency during your teens and twenties.
Cold sores (fever blisters) are caused by the herpes simplex virus, usually HSV-1. Unlike canker sores, they typically appear on or around the lips, start as fluid-filled blisters, and are highly contagious. Once you carry the virus, cold sores can recur throughout your life, often triggered by stress, sun exposure, or illness.
Oral thrush is a fungal infection caused by an overgrowth of a yeast called Candida albicans. It shows up as creamy white patches on the tongue or inner cheeks that can be wiped away to reveal reddened tissue underneath. A healthy immune system normally keeps this fungus in check, but when the balance between “good” and “bad” microbes is disrupted, the fungus can take over.
Other types include sores from accidental bites, burns from hot food, and irritation from braces or ill-fitting dentures. These are usually straightforward and heal quickly once the source of irritation is removed.
What Causes Them
Canker sores don’t have a single clear cause, which can be frustrating if you get them often. Instead, a combination of triggers tends to be responsible. Physical trauma like biting your cheek, brushing too hard, or dental work can set one off. Stress and lack of sleep are common triggers. Hormonal shifts during menstruation also play a role for some people.
Nutritional deficiencies are an underappreciated factor. Low levels of vitamin B12, folate, and iron are all linked to recurrent mouth ulcers. The NHS lists a sore or red tongue with mouth ulcers as a recognized symptom of B12 or folate deficiency anemia. If you’re getting canker sores frequently and can’t identify an obvious trigger, a nutrient gap is worth investigating.
Certain foods can provoke sores in susceptible people, especially acidic fruits like oranges and tomatoes, along with spicy dishes and rough-textured snacks like chips or crusty bread. Even your toothpaste may be a culprit. Sodium lauryl sulfate (SLS), a foaming agent found in most toothpastes, has been shown to increase the frequency and intensity of canker sores in people who are prone to them. Switching to an SLS-free toothpaste is one of the simplest changes you can make.
When Mouth Sores Signal Something Bigger
Occasional canker sores are rarely a sign of a serious problem. But recurrent or severe mouth ulcers can be a symptom of an underlying condition. Inflammatory bowel diseases like Crohn’s disease and ulcerative colitis are known to cause oral ulcers. Celiac disease, which is triggered by gluten, can produce mouth sores as one of its earliest signs. Behçet’s syndrome, a rare condition involving blood vessel inflammation, lists recurrent oral ulcers as a core diagnostic feature. Lupus can also cause sores in the mouth.
If your sores come with other unexplained symptoms, like digestive problems, joint pain, skin rashes, or fatigue, the mouth sores may be a visible piece of a larger puzzle.
How to Treat Mouth Sores at Home
Most minor mouth sores don’t require medical treatment and will heal within about two weeks. But you can ease the pain and potentially speed things up with a few straightforward steps.
- Salt water or baking soda rinse: Dissolve 1 teaspoon of baking soda in half a cup of warm water and rinse several times a day. Plain salt water works too.
- Milk of magnesia: Dab a small amount directly onto the sore a few times daily. It helps neutralize acid and coats the area.
- Over-the-counter numbing gels: Products containing benzocaine (like Orajel or Anbesol) temporarily numb the sore so you can eat and drink more comfortably.
- Hydrogen peroxide rinse: Mix equal parts hydrogen peroxide and water and rinse twice a day to keep the area clean.
- Avoid irritating foods: Stay away from acidic, spicy, and abrasive foods until the sore heals. Room-temperature or cool foods are gentler than hot ones.
Applying any topical product works best when you use it as soon as the sore appears. Waiting several days reduces the benefit. Staying hydrated and keeping your mouth clean with gentle brushing also supports faster healing.
Preventing Recurrent Sores
If you get canker sores regularly, prevention is more valuable than treatment. Start by switching to an SLS-free toothpaste. These products use milder surfactants like sodium cocoyl glutamate or sodium lauroyl sarcosinate, or rely on baking soda for cleaning. Many people who make the switch notice a significant drop in how often sores appear.
Pay attention to your diet. Make sure you’re getting enough B12 (found in meat, fish, eggs, and dairy), folate (leafy greens, legumes, fortified grains), and iron. If you follow a vegetarian or vegan diet, supplementation or fortified foods may be necessary to cover gaps in B12 specifically.
Track your triggers. Keep a simple log when a sore appears: what you ate the day before, how stressed you were, where you are in your menstrual cycle if applicable, and whether you had any mouth trauma. Patterns often become obvious within a few months. Some people find that a specific food, like walnuts or chocolate, reliably triggers a sore within a day or two.
Signs That Need Professional Attention
A mouth sore that lasts longer than two weeks without showing signs of healing is the clearest signal to get it checked. Other situations that warrant a call to your doctor or dentist include sores that are larger than a centimeter (roughly the size of a pea), sores that come back two or three times a year, sores accompanied by flu-like symptoms, and sores that interfere with your ability to eat or drink.
Persistent sores that don’t heal are also one of the early warning signs of oral cancer. Non-healing ulcers, unexplained lumps, and changes in the color or texture of mouth tissue all warrant evaluation. Oral cancers can sometimes present without pain, which means the absence of discomfort doesn’t rule out a problem. A sore that simply won’t go away, even if it doesn’t hurt, deserves attention.