Acute nephritis indeed tends to cause "fire-up," which refers to the viral infection in patients. Typically, the appearance of herpes on the upper lip is colloquially known as "fire-up," but in reality, this is an active manifestation of the herpes virus when the body's immune capacity is low. The human body often carries this virus, and symptoms appear when immunity is low. In the state of acute nephritis, it is easy to result in reduced immunity in patients, thus activating the dormant virus in the body, causing herpes in corresponding areas including the upper lip and corners of the mouth.