A mouth ulcer occurs when a part of the lining of the inside of your mouth becomes damaged. The area that hurts is known as a mouth ulcer. They are very common and can be caused by many different things. The majority are not caused by anything serious and will improve on their own within 2 weeks. They look like red and white lesions on the inside of your cheeks that are usually less than ½ inch in size. You can sometimes get larger mouth ulcers which can appear at the bottom of the gums, under or on the tongue. Most people have at least one attack of mouth ulcers in their life but they are more common in women and under the age of 40. They cannot be passed on by kissing or sharing utensils. Unfortunately, up to 1 in 5 people have recurrent attacks of mouth ulcers. Over a third of people with recurrent mouth ulcers have a family history of it and this figure rises to over 80% if both parents suffered from recurrent mouth ulcers. Certain medical conditions can also predispose to chronic mouth ulcers developing, such as: Vitamin B12 deficiency. Viral infections – a very common trigger for mouth ulcers. Iron deficiency. Celiac disease (intolerance to a protein called gluten, found in wheat, rye and barley). Crohn's disease. Reiter's syndrome. HIV infection. Occasionally, mouth ulcers can be linked to medication and common examples include: Painkillers such as ibuprofen and aspirin. Nicorandil and beta blockers – both used in heart conditions.

Oral thrush is a yeast infection of the mouth. It is very common in children and babies and can be common in people who wear dentures or those who are prone to infections due to other medical conditions. Certain medications can put you at higher risk of developing oral thrush, including taking a course of antibiotics or using an asthma inhaler that contains a steroid. If you have oral thrush, you will usually have a mouth that is more red than usual, with white patches over the top. The white patches can be rubbed off and may lead to slight bleeding underneath if you do so. Oral thrush can cause pain and changes to your taste, it may be sore when you eat and drink, and babies can be reluctant to start or continue feeding as it is painful.

Angular cheilitis is a condition that mainly affects the corners of the mouth rather than the rest of the lips. The main symptoms include swelling and redness, blistering, and crusting or cracking in the corners of the mouth. It may be painful and can be caused by a number of factors. Some forms of angular cheilitis may be caused by sweat and saliva build-up. This causes changes in pH on the skin and can lead to a fungal infection in the corners of the mouth. There can also be bacterial or viral infection present. It is usually bilateral and symmetrical, although occasionally it may affect one side of the mouth only and may sometimes spread to cause impetigo or oral thrush.