Canker sores, unlike the similar-sounding syphilis chancre, are not STDs. In fact, they are not contagious at all. Instead, they are linked to various nutritional deficiencies as well as certain immune problems.
Canker sores are more common in individuals who are immunocompromised, such as individuals with HIV.
Although canker sores do not generally require medical treatment, there are exceptions. If you have a canker sore that is particularly large, particularly painful, takes longer than three weeks to heal, or comes along with a high fever, make an appointment with your doctor. That way she can determine if your canker sore may be the result of a more serious underlying health problem.
