Why is Soap the most effective way of killing Coronavirus on the skin?

Once you touch a surface where the virus is active, the virus will stick to your skin and this is where the virus will easily spread if you touch your eyes, nose or mouth, which is where you may become infected. The most efficient way of killing the virus on the skin is soap and water, soapy water works by dissolving the virus’ fat membrane which makes the virus break down.

Washing your hands regularly with soap and water is the best way to Kill the Coronavirus and to help prevent the virus from spreading. Although hand sanitisers can be an effective method of killing the virus soap and water is the most efficient. 

The Science of Soap - Here's how it kills the Coronavirus by Pall Thordarson is a Professor in Chemistry at the University of New South Wales, Sydney
https://www.theguardian.com/commentisfree/2020/mar/12/science-soap-kills-coronavirus-alcohol-based-disinfectants