Hand sanitizers don't necessarily work as well as soap and water. The effectiveness of alcohol-based gels like Purell depends on the type and amount of germs that they are up against. In general, the longer it's been since you've washed with soap and water, the less effective a hand sanitizer is likely to be. Proteinaceous and fatty materials (commonly found in any kitchen) are especially resistant to alcohol-based gels. The Centers for Disease Control guidelines that recommended hand sanitizers as a suitable alternative to hand washing were intended only for health-care settings, where doctors and nurses wash their hands several times an hour, providing the gels with a relatively clean surface to work on.