In the wake of the COVID-19 coronavirus outbreak, many of us are stocking up on hand sanitizers to keep clean. That's great! But using Purell is no substitute for thorough and regular hand washing.

Actress Kristen Bell recently published a set of black light comparison photos showing how clean her hands become during various stages of hand washing. As you can see from the pictures, it takes 30 seconds of soapy washing to completely clean the hands.

The CDC recommends washing hands for at least 20 seconds, but it never hurts to be sure.

The BusinessInsider folks followed up on this finding with their own UV light test, showing the difference between hands washed with hand sanitizer alone and hands washed with soap for 30 seconds The difference between the two images was quite striking, with hands washed with sanitizer still showing many visible germs, but hands washed with soap hands washed with soap were almost completely free of dirt.

As BusinessInsider points out, hand sanitizers neutralize bacteria but do not kill them. Since hand sanitizers still kill many bacteria, it is worth keeping them on your desk to keep your hands sterilized from daily touches at work and at home.

So when you stock up on bottles of Purell (or whatever hand sanitizer you can still get your hands on), be sure to have plenty of regular hand soap on hand as well. Also, remember to disinfect your surroundings, cover your coughs and sneezes with tissues, and limit your time in social settings.