A sore in your mouth is your body’s way of signaling that something has gone wrong on the thin, sensitive tissue lining your lips, cheeks, gums, tongue, or throat. Most mouth sores come from one of a few common causes: minor injury, a viral infection like herpes simplex, an immune reaction such as a canker sore, a nutritional deficiency, or irritation from food and chemicals. The type of sore, where it sits, and how long it lasts usually point to the trigger.
What Causes Sores In Your Mouth Types Triggers?
The single most common cause is trauma. You bite your lip, burn your mouth on hot pizza, or scrape your gum with a sharp chip. The tissue breaks, and a sore forms. These usually heal on their own within a week or two.
The second major category is immune-related. Canker sores, also called aphthous ulcers, are not caused by a virus or bacteria. They are an inflammatory response. The immune system attacks the lining of the mouth for reasons that are not fully understood.
The third category is infectious. Herpes simplex virus type 1 causes cold sores, which typically appear on or near the lips. Other viruses, bacteria, and fungi can also produce sores inside the mouth.
Nutritional deficiencies, certain medications, and underlying medical conditions round out the list. In many cases, more than one factor is at play.
What Is the Difference Between a Canker Sore and a Cold Sore?
These two get confused constantly, and the difference matters because the causes and contagiousness are completely different.
A canker sore forms inside the mouth. You will find it on the tongue, the soft palate, the inside of the cheek, or the base of the gums. It has a white or yellow center with a red border. It is not contagious. You cannot pass a canker sore to another person through kissing or sharing utensils.
A cold sore is caused by the herpes simplex virus, usually type 1. It typically appears on the outer lip, the corner of the mouth, or the skin around the mouth. It starts as a tingling or burning sensation, then forms a cluster of small blisters that crust over. Cold sores are contagious, especially when blisters are present. The virus stays in the body for life and can reactivate during stress, illness, sun exposure, or a weakened immune system.
Some people get herpes sores inside the mouth, but this is less common and usually happens during a first infection. A doctor can tell the difference if there is any doubt.
What Triggers Canker Sores to Flare Up?
Canker sores have a long list of possible triggers. Not everyone reacts to the same ones, and for many people no clear trigger is ever identified.
Common triggers that research and clinical experience point to include:
- Minor mouth injury from dental work, brushing too hard, or accidental biting
- Certain foods, especially acidic ones like citrus, tomatoes, and pineapple, or spicy foods
- Stress and lack of sleep
- Nutritional deficiencies, particularly vitamin B12, iron, folate, and zinc
- Hormonal changes, including those related to menstruation
- Toothpaste or mouthwash containing sodium lauryl sulfate
- Certain medications, including some anti-inflammatory drugs and beta-blockers
- Stopping smoking, which can trigger a temporary flare
The evidence for some of these triggers is stronger than for others. Sodium lauryl sulfate, a foaming agent in many toothpastes, has been studied as a canker sore trigger. Some research suggests switching to an SLS-free toothpaste may reduce how often sores appear, though results vary. Nutritional deficiencies are well-established contributors, especially in people with recurrent canker sores.
When Do Mouth Sores Signal Something More Serious?
Most mouth sores are minor and resolve on their own. But some are the first sign of a condition that needs medical attention.
See a doctor or dentist if a sore:
- Lasts longer than two weeks
- Keeps getting bigger or spreads
- Bleeds easily or feels hard at the edges
- Comes with fever, weight loss, or difficulty swallowing
- Appears alongside sores on the skin, eyes, or genitals
Recurrent canker sores can be linked to conditions like Behçet’s disease, inflammatory bowel disease, or celiac disease. A sore that does not heal could be a sign of oral cancer, especially if it is painless and has a raised or irregular border. Oral cancer is not common, but early detection makes a significant difference.
Mouth sores can also be a side effect of medications, including some chemotherapy drugs and immunosuppressants. If you are undergoing treatment and develop sores, tell your care team.
What Nutritional Deficiencies Cause Mouth Sores?
Several vitamins and minerals play a direct role in maintaining the health of the mouth’s lining. When levels drop, the tissue becomes more vulnerable to breakdown and slower to repair.
The deficiencies most consistently linked to mouth sores are:
- Vitamin B12 — needed for cell division and repair
- Folate — works with B12 in tissue maintenance
- Iron — low levels can cause a sore, smooth tongue and cracks at the corners of the mouth
- Zinc — supports wound healing and immune function
- Vitamin C — severe deficiency (scurvy) causes bleeding gums and poor healing
A blood test can check for these deficiencies. If a deficiency is found, correcting it may reduce how often sores appear. But taking supplements without a confirmed deficiency is unlikely to help and can cause harm in some cases.
Are Mouth Sores Contagious?
It depends entirely on the cause. Canker sores are not contagious. Cold sores are highly contagious, especially when blisters are visible. Hand, foot, and mouth disease, which causes sores in the mouth and a rash on the hands and feet, is caused by viruses that spread easily through saliva, nasal secretions, and contact with blister fluid.
Herpes simplex can spread even when no blisters are visible, though the risk is highest when sores are present. Avoid kissing, sharing utensils, or sharing towels with someone who has an active cold sore.
If you have a sore and are not sure what caused it, treat it as potentially contagious until you know otherwise. That means no sharing drinks, utensils, or lip products.
What Helps Mouth Sores Heal?
Most minor sores heal without treatment in one to two weeks. The goal of treatment is usually to reduce pain and, in some cases, shorten the duration.
For canker sores, over-the-counter topical products containing benzocaine or other numbing agents can reduce pain. Some clinicians recommend a rinse of salt water or baking soda in water to keep the area clean. Prescription treatments, including topical corticosteroids, may be used for severe or recurrent cases.
For cold sores, antiviral medications like acyclovir or valacyclovir can shorten healing time and reduce pain if started early. These are available by prescription. Over-the-counter creams may provide some relief but do not kill the virus.
Avoiding trigger foods, using a soft-bristled toothbrush, and managing stress may help reduce how often sores appear. If you have a confirmed nutritional deficiency, correcting it is important.
No treatment currently cures herpes simplex or prevents canker sores entirely. If you get sores frequently, a doctor can help identify underlying causes and discuss options.
Frequently Asked Questions
What is the most common cause of mouth sores?
Minor injury is the most common cause. Biting your lip, burning your mouth, or scraping your gum can all lead to a sore that heals on its own within a week or two.
How long should a mouth sore last before I see a doctor?
See a doctor or dentist if a sore lasts longer than two weeks. Sores that keep growing, bleed, or come with fever or difficulty swallowing also need medical attention.
Are mouth sores a sign of a vitamin deficiency?
Sometimes. Deficiencies in vitamin B12, folate, iron, or zinc are linked to recurrent mouth sores. A blood test can confirm whether a deficiency is present.
Can stress cause mouth sores?
Stress is commonly reported as a trigger for canker sores, though the exact mechanism is not fully understood. Lack of sleep and stress may both play a role in flare-ups.
