Stomatitis is an inflammation of the lining of the mouth that causes pain, ulcers, and bleeding. It can be caused by poor oral hygiene, medications, infections, nutritional deficiencies, or other issues. Symptoms include pain, ulcers, fever, irritability, swollen or bleeding gums, and bad breath. Treatment focuses on identifying and addressing the underlying cause, using pain medications, antiviral drugs for infections, and maintaining good oral hygiene.