Zovirax is a brand name for a cream containing the active ingredient acyclovir, which belongs to a class of antiviral medications called nucleoside analogues. It is used to treat cold sores and genital herpes caused by the herpes simplex virus (HSV). Acyclovir works by stopping the herpes virus from replicating and spreading to healthy cells in the body. It does not cure herpes infections but helps to reduce the severity and duration of outbreaks and speeds up the healing process of sores. Zovirax cream should be applied directly to the affected area(s) of the skin, usually 5 times per day for 4 days. It is important to start using the cream as soon as possible after the first signs of a cold sore or genital herpes appear, such as tingling, burning, or itching. The cream should be applied using a clean finger or cotton swab, and hands should be washed thoroughly before and after application to prevent the spread of infection. Zovirax cream is generally safe and well-tolerated, but like all medications, it can cause side effects. Some common side effects include mild burning, stinging, or itching at the application site. Serious side effects are rare but may include allergic reactions, rash, hives, difficulty breathing, or swelling of the face, lips, tongue, or throat. If you experience any of these serious side effects, seek immediate medical attention. Zovirax cream is not recommended for people who are allergic to acyclovir or any of its ingredients, and it should be used with caution in people with kidney problems or a weakened immune system. It is important to talk to your healthcare provider before using Zovirax cream if you are pregnant, breastfeeding, or have any medical conditions or are taking any medications. Zovirax cream is a prescription medication, and it is important to use it only under the supervision of a healthcare provider.