Aciclovir Cream IP 5% w/w is a topical antiviral medication used for the treatment of skin infections caused by the herpes simplex virus (HSV), including cold sores (herpes labialis) and genital herpes. It contains 5% w/w of aciclovir, a guanine nucleoside analog that works by inhibiting viral DNA replication. When applied to the affected area, aciclovir penetrates infected skin cells and interferes with the growth and spread of the virus, helping to reduce the severity, duration, and pain of outbreaks.