The most common sites for canker sores are the movable parts of the mouth such as the inside lining of the lips and cheeks and the tongue. In certain cases even the palate can be affected. In its earliest stage, the ulcer begins as small round reddish swelling that usually burst within a day, exposing raw mucous membrane. Shortly after the rupture, the sore appears to be covered with a thin yellow white and visibly highlighted by a red halo of inflammation which endures until the healing is complete.

If you have canker sores, avoid abrasive foods such as potato chips that can stick in the cheek or gum and aggravate the sores. Take care when brushing your teeth not to stab the gums or cheek with a toothbrush bristle. Avoid acidic and spicy foods. A canker sore (medically referred to as aphteous ulcer), is a type of oral ulcer that results from the breakage of the oral mucous membrane and presents itself as a painful open sore. This condition is also known as aphteous stomatitis especially in the case of multiple or recurring ulcers. About 20 percent of the population, or one out of five people, have these ulcers at any one time.

The frequency of canker sore recurrences varies considerably from a few episodes per year to a continuous multiple recurrent series of ulcerations. Women are more susceptible to have recurrent canker outbreaks. Female hormones affect aphtheous ulcers and it is common for some women to experience multiple outbreaks during menstruation. However, hormonal changes caused by pregnancy usually induce temporary relief from the painful ulcers. Some genetic studies point out that susceptibility to aphteous ulcers is an inherited trait explaining why some family members share this condition. If ulcers are extremely slow to heal or other associated systemic symptoms are present, other more serious conditions should be ruled out by a primary care physician. Aphteous ulcers are a poorly understood clinical entity that may cause significant pain in otherwise healthy patients.

Nobody really knows what causes mouth ulcers, menstruation, sodium laurel sulfate in certain toothpastes, high nitrate levels in water have all been linked to it. Emotional stress and traumatic injuries are common triggers to the outbreak of ulcers.