Aphthous Mouth Ulcers: Types, Triggers and When to Get Them Checked

An aphthous ulcer is a shallow, round or oval sore with a pale yellow or grey centre and a red border. It appears on the inside of the lips and cheeks, under the tongue, or on the soft floor of the mouth, and it hurts out of proportion to its size, especially with spicy, salty or sour food. The medical term aphthous stomatitis simply means this recurring pattern of ulcers.

The exact cause is not fully understood. It is not caused by a germ, so you cannot pass it on by kissing or sharing a cup. People who get them repeatedly often have a family history, and episodes tend to cluster around stress, poor sleep, a cheek bite or a hormonal change.

Ulcers that sit in one spot and match a sharp tooth edge, a broken filling or a rubbing denture are a different problem: they are caused by injury, and they stop once the irritant is smoothed or fixed.

The three types differ mainly in size, number and healing time. Minor ulcers are by far the commonest. Major ulcers are rarer, larger and deeper, and can leave a scar. Herpetiform ulcers have nothing to do with the herpes virus despite the name; they just look like a cluster of tiny pinpoint sores.

If your ulcers are crops of small blisters on the gums or palate with a fever, that is more likely a viral infection, covered in our guide on herpetic ulcers in the mouth.

Known triggers include stress, a minor injury inside the mouth, hormonal changes around periods, and certain foods such as very spicy, acidic or sharp-edged ones in people who are prone. Some people notice that toothpastes containing sodium lauryl sulphate make ulcers worse and do better on a toothpaste without it.

Low iron, vitamin B12 or folate can also sit behind frequent ulcers. If yours keep coming back, a blood test is more useful than guessing, and our guide on mouth ulcers and vitamin deficiency explains who is at risk.

While an ulcer is healing, the aim is comfort. Rinsing with warm salt water, avoiding the foods that sting and using a protective or numbing gel as directed on the label all help; the mouth ulcer home remedies guide sets out what works and what does not.

The rule that matters is on our mouth ulcers page: an ulcer that has not healed within three weeks needs examining, whether or not it hurts. Painless ulcers that refuse to heal, or that have hard or raised edges, are the ones that deserve the most attention, especially in people who chew tobacco, gutkha or supari.

See a dentist or doctor sooner if ulcers keep returning, are very large, make eating or drinking difficult, or come with fever, a rash or ulcers elsewhere in the body.