These sores are
small ulcers inside the mouth. They have a
white or gray base and a red border. Women
are more likely than men to have canker sores
that recur. The cause of canker sores is
unknown. Risk factors include:
Fatigue
Stress
A cut on the inside of your cheek or on your
tongue
Allergies
Canker sores most often heal on their own in
one to three weeks. See your dentist if you
get a large sore (larger than a half inch, or
about the size of a dime).