Oral Herpes Simplex: Symptoms and Prevention Oral herpes simplex is a contagious infection that affects the mucous membranes in and around the mouth, caused by the herpes simplex virus. Recognizing its symptoms can aid in early detection and treatment, including oral mucosal blisters and skin lesions around the mouth. Oral Mucosal Blisters: These are the most characteristic signs of oral herpes simplex. Initially, clusters of small, thin-walled, and transparent blisters appear on the oral mucous membranes, surrounded by a red halo. These blisters can occur anywhere on the oral mucous membranes, such as the lips, cheeks, tongue, and gums. They... Learn more