While the last 100 years have seen amazing advancements and innovations in medicine, the best way to keep from getting sick or spreading illness is the same as it was a century ago: regularly washing your hands with soap and warm water.

I know, it's not very exciting or cutting edge. Dull as it may be, though, hand-washing is the cornerstone of sickness prevention because so many communicable diseases are transmitted by our hands.

While using old-fashioned soap and warm water is the best way to reduce the amount of germs on your hands, there's another method that continues to grow in popularity.

It seems like almost everywhere you go in the United States these days, there's a big dispenser of hand sanitizer hanging on the wall -- in grocery stores, shopping malls, airports. The wide availability of hand sanitizer is a boon for public health. Alcohol-based sanitizers are very effective at killing many germs that make us sick, and they're a great option when soap and water aren't available.

However, hand sanitizers have their limits. They don't eliminate all types of germs, including some that can make people very sick. So it's important to understand what hand sanitizers can do and what they can't.

First, let's talk about what they can do. (To avoid confusion, I'm talking about alcohol-based hand sanitizers, not other kinds of sanitizers.)

Hand sanitizers kill all kinds of harmful bacteria and viruses, including flu viruses. Just make sure you're using a sanitizer that contains 60 percent alcohol or more, otherwise it's not potent enough to kill those harmful germs.

Another thing to keep in mind is that hand sanitizers are effective only if they're used correctly. If you don't use enough hand sanitizer, it won't clean your hands as well.

How much is enough? I suggest applying at least a dime-sized amount, enough so that when you rub your hands together it will cover all areas of your hands, including under your nails. Use a rubbing motion to evenly distribute the sanitizer product for about 15 seconds or until your hands feel dry.

But even if you use hand sanitizers correctly, they won't be effective in certain circumstances. Alcohol-based sanitizers are not effective on visibly dirty hands. If you can see dirt on your hands, use soap and warm water.

And as I mentioned earlier, hand sanitizers don't kill all types of germs. For instance, hand sanitizer doesn't kill norovirus, which causes stomach pain, nausea, diarrhea and vomiting -- sometimes for several days.

Norovirus is highly contagious and spreads from person to person through contaminated food, water and objects that come in contact with the mouth. Soap and warm water are your best weapons against norovirus.

Despite the limitations of hand sanitizer, it's still a great tool to protect yourself against germs. One great thing about it is the portability. You can easily stick a bottle into a backpack, purse or jacket pocket when you're on the go. Sanitizers also don't dry out your hands as much as soap and water.

Just remember that hand sanitizers are not a substitute for washing with soap and warm water. They're a good supplemental tool to the old-fashioned method that has worked for hundreds of years.

For more information about hand hygiene, visit cchealth.org/hand-washing

Susan Farley is the communicable disease controller for the Public Health Division of Contra Costa Health Services. Healthy Outlook is written by the professional staff of the county health department. Send questions to series coordinator Dr. David Pepper at theairdoctor@gmail.com. For more health information, go to www.cchealth.org.

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