What causes fever blisters on the mucous membrane of the lip or mouth?

Fever blisters, also known as cold sores, are primarily caused by the Herpes Simplex Virus (HSV), specifically HSV type 1. The infection usually occurs first in childhood or early adulthood and can remain dormant in the body after the initial episode. When the virus reactivates, often due to factors like stress, illness, or sun exposure, it leads to the painful vesicular lesions on the mucous membranes of the lip or mouth.

The presence of the herpes simplex virus explains why fever blisters are so common and can recur throughout a person's life. While dehydration, heat exposure, and fungal infections can impact oral health in various ways, they do not specifically cause the characteristic blisters associated with the herpes simplex virus. Understanding the role of the herpes simplex virus is crucial for recognizing, preventing, and managing fever blister outbreaks effectively.