The two most common types seen in children are herpes stomatitis, which is caused by the herpes simplex virus, and aphthous stomatitis, more often referred to as canker sores.
There may be an inherited tendency to develop canker sores and there may also be an immune system link.
Sodium lauryl sulfate (SLS), a component of some toothpastes, is a potential cause of canker sores.
In one study, most recurrent canker sores were eliminated just by avoiding SLS-containing toothpaste for three months.
Parents may also use Oragel, an ointment often used for canker sores or teething.