My husband keeps getting a huge canker sore in the back of his mouth, almost throat . it goes away and comes back. what could be causing it?

See a dentist: Recurrent sores must be evaluated to rule out possible major or serious problems. This forum does not give us enough information to know exactly what the problem is, seeing the patient directly is beneficial in making a diagnosis. See your dentist or oral surgeon asap.

A virus: A good economical fix is to go to your local pharmacy an buy a product called zilactin. Dry the ulcer with cotton tip applicator the apply a small pea sized drop of the gel. Wait until the gel becomes opaque. Plain zilactin stings. Zilactin recognized this and added Benzocaine to their product. The mixture is called zilactin b. You might have a vitamin deficiency. Check with your primary care.