A mouth ulcer occurs due to loss of the inner lining of the oral cavity. It may be single or multiple, small or big. Ulcers can occur on the inside of the cheek, above or below the tongue, on the gums, or on the palate. They are mostly red, white, or yellowish. Irrespective of the size or number of ulcers, it causes discomfort and pain when eating and or drinking. Discomfort is more with hot food and drinks. Though it is painful and sometimes frightening for the affected person, most of them are benign and harmless. There are multiple reasons for mouth ulcers. The most common cause is accidental bite by the teeth while eating. Irritation by a loose tooth or denture, and loose cavity fillings, can cause ulcers in the oral cavity. Very hot or spicy food can also irritate the inner lining of the mouth. Ulcers may occur due to acidic food substances, such as pineapple, strawberries, etc. Sometimes, it may be due to an allergy to the food substance or drink being consumed. A deficiency of vitamin B12 and vitamin B5 causes oral ulcers as one of the manifestations. Chronic constipation and digestive problems may induce mouth ulcers. A toothbrush with harsh bristles or abrasive toothpaste are some other factors that can cause mouth ulcers. Women may develop oral ulcers due to hormonal changes around menses. Some individuals have oral ulcers due to stress or lack of sleep. Aphthous ulcers are recurring oral sores, and their exact cause is unknown. However, they are harmless. Certain fungal, bacterial, or viral infections can cause mouth ulcers as one of the manifestations. Diseases like tuberculosis, syphilis, and some autoimmune diseases, may have oral ulcers as one of their manifestations. They can be caused by certain painkillers, immune suppressive drugs, and some antihypertensive drugs as adverse effects. Rarely, antibiotic use may cause oral ulcers, by causing digestive problems. Cancer is a sinister cause of mouth ulcers. Prevention of mouth ulcers involves eating a healthy nutritious diet, getting adequate sleep, and avoiding stress. One should avoid very hot, spicy food and drinks. Drinking 8 to 10 glasses of water per day and a high-fibre diet are measures that help prevent and cure constipation, other digestive problems, and resultant oral ulcers. The diet should include fresh fruits, green vegetables, whole grains, and milk products like yoghurt and cheese. Any loose tooth, denture, dental filling, etc. should be remedied at the earliest. One should avoid using a toothbrush with harsh bristles. Kinds of toothpaste that contain ingredients to whiten the teeth or remove dental stains are more abrasive than others. Calcium carbonate, sodium metaphosphate, and zirconium silicate are some of the ingredients that are abrasive in kinds of toothpaste. Most of the oral ulcers heal by themselves spontaneously in a week or so. Correction of the underlying cause cures the oral ulcers very well. Saline mouthwash, with or without sodium bicarbonate, helps to maintain oral hygiene, soothes mouth ulcers, and prevents infection in the oral cavity. This helps in healing existing ulcers and preventing mouth ulcers as well. Drinking tepid water is soothing for the mouth, as compared to hot or cold water. Antiseptic mouthwashes are also helpful in this regard. Some antibiotics help in healing aphthous ulcers. Application of local anesthetic and or steroid tablets are useful in the cure of aphthous ulcers. Supplements of vitamin B complex, particularly B5, B9, and B12, can aid in healing mouth ulcers, particularly if due to a deficiency of vitamin B complex. However, if the mouth ulcers are recurrent, or persistent, if there is an increase in size and number, if there is persistent pain, or if mouth ulcers become red and painful, medical advice should be sought. Clinical examination and suitable investigations can diagnose cancer of the mouth. Dr Rachna Pande is a specialist in internal medicine.