My 12 yr old son has 5 mouth ulcers right now. what causes that and how can i treat them?

Virus: Many viruses cause mouth ulcers. They go away by themselves. Treatment is to decrease pain with analgesics and maintain good oral hygiene.

Apthos Ulcers: Aphthous ulcers can result from many things, including certain foods, immune disorders, tissue trauma, emotional stress or nutritional deficiencies. While there isn't a cure, they can be treated with a soft tissue laser to help the sore heal faster and alleviate the painful symptoms. Topical gels like orajel can also help to reduce the pain.