Mouth sores are very common, and most are harmless and temporary, but some can signal infections or other medical conditions, so any sore that is severe, keeps coming back, or lasts more than 2 weeks should be checked by a doctor or dentist.

Common reasons you have mouth sores

Mouth sores can show up on the tongue, inside the cheeks, on the gums, lips, or the roof or floor of the mouth, and the cause often depends on where they are, what they look like, and how long they last. Below are some of the most frequent causes people run into.

  • Minor injury or irritation
    • Biting your cheek, tongue, or lip.
    • Brushing very hard or using a hard-bristled toothbrush.
    • Rubbing from braces, retainers, sharp or broken teeth, or poorly fitting dentures.
    • Burning your mouth with hot food or drinks, or irritation from very acidic/spicy foods.
      These small injuries can break the surface of the lining in your mouth and turn into painful sores as they heal.
  • Canker sores (aphthous ulcers)
    • Usually small, round or oval, with a white, yellow, or gray center and a red border.
    • They form inside the mouth (cheeks, tongue, inside lips, soft palate), not on the outer lip.
    • Often linked to triggers like stress, hormonal changes, minor trauma, or vitamin deficiencies (like iron, B12, folate) and can run in families.

They are not contagious but can be quite painful, especially when eating or talking.

  • Cold sores (fever blisters)
    • Caused by the herpes simplex virus, which stays in the body and can flare up again.
    • Often start with tingling, burning, or itching around the lip, then form clusters of blisters that crust over.
    • Very contagious through kissing or sharing items like utensils or lip balm.
      Triggers include stress, sun exposure, illness, or a weakened immune system.
  • Fungal or other infections
    • Oral thrush (candidiasis) causes white, creamy patches that may wipe off and leave a red, raw surface underneath.
    • Viral illnesses like hand-foot-and-mouth disease, mono, or other viral infections can cause multiple sores and flu‑like symptoms.
    • Bacterial gum infections can create painful ulcers or inflamed areas.
      These are more common if your immune system is weakened, you use inhaled steroids without rinsing, or you’ve recently used antibiotics.
  • Irritants, allergies, and lifestyle factors
    • Tobacco (smoking or chewing) irritates the lining and raises the risk of chronic sores and oral cancer.
    • Alcohol and very spicy or acidic foods can inflame tissues in some people.
    • Some toothpastes or mouthwashes (for example, those with sodium lauryl sulfate) may trigger canker sores in sensitive mouths.
      Repeated irritation in the same spot is a reason to have it examined.
  • Medications and medical treatments
    • Certain antibiotics, pain medicines, and other prescription drugs can cause mouth ulcers as a side effect.
    • Chemotherapy and radiation to the head and neck frequently lead to painful mouth sores (mucositis).
      Always tell your doctor if new mouth sores appear after starting or changing a medication.
  • Underlying health conditions
    • Autoimmune diseases (like lupus, Behçet disease, inflammatory bowel disease, or celiac disease) can cause recurrent or persistent mouth ulcers.
    • Blood and immune problems, including nutritional deficiencies (iron, B12, folate) and immune suppression (for example, HIV or medicines after organ transplant), can also show up as frequent sores.
    • In some cases, non‑healing or unusual sores are a sign of oral cancer.
      These situations usually involve other symptoms such as fatigue, weight loss, fevers, or swollen glands.

When to worry and see a doctor or dentist

Most simple mouth sores heal on their own in 7–14 days, but some red flags mean you should seek in‑person care quickly.

  • Get urgent or same‑day care if:
    • You have trouble breathing, swallowing, or opening your mouth.
    • Your tongue or throat is swelling.
    • You have a high fever, feel very unwell, or have a stiff neck.
  • Make a prompt appointment with a dentist, doctor, or urgent care if:
    • A sore lasts more than 2 weeks, keeps growing, or keeps bleeding.
    • You have many sores at once, or they keep coming back frequently.
    • The sore has hard, raised, or irregular edges, or there is a red or white patch that does not go away.
    • You use tobacco or drink heavily and notice a new, persistent patch or lump in your mouth or on your lip.
    • You also have weight loss, night sweats, or persistent swollen lymph nodes in your neck.

These signs do not automatically mean something serious, but they do mean a professional needs to look closely.

What you can do at home (short term)

Home care cannot replace a proper exam, but it can ease discomfort while you arrange to be seen, especially if your sores seem minor.

  • Gentle mouth care
    • Use a soft‑bristled toothbrush and brush slowly.
    • Avoid mouthwashes with alcohol; choose a mild or salt‑water rinse instead.
  • Rinses and soothing measures
    • Rinse several times a day with warm salt water (about half a teaspoon of salt in a cup of warm water, then spit).
    • Cold items like ice chips, chilled water, or cold soft foods can reduce pain briefly.
  • Avoid triggers
    • Skip spicy, salty, or acidic foods (for example, citrus, chips, salsa) until sores heal.
    • Avoid tobacco and alcohol, both of which slow healing.
  • Over‑the‑counter help (ask a pharmacist if unsure)
    • Protective gels, pastes, or patches designed for mouth ulcers can cover the sore to reduce friction.
    • Pain relief lozenges or topical numbing gels can be used short term as directed on the package.

If you already know you have conditions like anemia, celiac disease, or autoimmune disorders, keeping those well controlled can reduce how often you get sores.

Why checking in person matters

A screen‑based explanation cannot see the size, shape, or exact location of your sores, and those visual details are what clinicians rely on to distinguish harmless ulcers from infections, allergic reactions, or early cancers. Because of that, any persistent, severe, or unusual sore in your mouth is safest handled by a dentist, primary‑care clinician, or urgent‑care provider who can examine you directly and order tests if needed.

If you describe where the sores are, how long they have been there, what they look like (color, shape, number), and any other symptoms (fever, weight change, fatigue, new medicines), a more tailored explanation of likely causes and next steps can be offered.