Fusiwal-B cream is not a medicine that directly treats the chickenpox virus itself. It contains an antibiotic and a mild steroid, and doctors sometimes prescribe it after chickenpox lesions start drying if they feel there is irritation, inflammation, or a secondary bacterial infection in the skin caused by scratching. That is likely why your doctor advised it. However, this cream should only be used exactly as prescribed and usually for a short duration, because steroid-containing creams are generally not used routinely on active viral infections like chickenpox unless a doctor feels the benefits are greater than the risks. If your chickenpox lesions are already drying and crusting, the cream may help reduce redness, itching, or infection in selected areas. Avoid applying it over fresh blisters, open wounds, or large areas without medical advice. Keep the skin clean, avoid scratching, trim your nails, and wear loose cotton clothes to help with healing. Calamine lotion and antihistamines are more commonly used for itching relief in chickenpox. If you notice increasing redness, pus, swelling, fever, worsening rash, or burning after applying the cream, stop using it and contact your doctor. Since your treating doctor has examined your skin directly, it is safer to follow their guidance rather than relying only on internet information, but it is completely reasonable to ask them why the cream was prescribed and for how long it should be used.