Center For Disease Control and Prevention (CDC) says that 20 seconds is the safe time limit to remove harmful germs and chemicals from your hands. A shorter time may not be sufficient enough to remove all germs.  This is because hands have a lot of cracks and crevices. Viruses thrive on being able to inhabit tiny spaces, abundant on the hands.  Washing for 20 seconds gives the soap and water molecules enough time to get into all of these spaces. Therefore, scrub all areas of your hands, including palms, backs of the hands, between the fingers, and under the fingernails in 20 seconds.