Hi, my friend often have mouth ulcers, which we suspect is a mixture of apathous and herpetiform ulcers. is there any reason behind it and any cure?

No cure: Unfortunately there is no cure, just treatment. Some medications to lessen the pain and duration, some foods to avoid, and maybe treat with laser to accelerate the healing. Seek your dentist's advice.

Dont suspect: First, start by having your friend see a dentist when the ulcers are present to be sure what it is. One has to start with a definitive diagnosis and not a guess. It may be other things as well. Once you know what it is, one can address prevention, treatment or acceptance. It's poor medicine and a disservice to patients to offer advice on guesses and undiagnosed lesions.

Stress: I agree that a biopsy should be done to find out what the lesion is. Most texts teach that outbreaks can be related to physical or psychological stress.