Small, shallow, and painful ulcers in the mouth are called canker sores. These kinds of sores most often occur on the tongue, inside the cheeks, gums, and inside the lips. Usually, these sores are round shaped, small, have a red border and have a white or yellow center to them. Sometimes canker sores can be so painful that talking and eating are difficult. These sores usually last anywhere between seven and fourteen days. When an individual has a particularly severe case of canker sores, they may experience a fever, swollen lymph nodes, and physical sluggishness.
While canker sores can be caused by a number of things, a niacin deficiency is strongly associated with recurrent canker sore outbreaks. The exact mechanism of how niacin deficiency causes these sores to form is still unclear, however, research has suggested it is because niacin plays a key role in cell production and hormone regulation, both of which can trigger the immune system to kick into a state of overdrive where it attacks its own tissues in the mouth. Canker sores most often resolve easily on their own, however, recurrent episodes of painful canker sores can cause the niacin deficiency to worsen.