• Alcohol-based hand sanitisers may kill a broad spectrum of bacteria and viruses, but it isn't effective on all germs.
  • Healthcare professionals recommend washing with soap and water over using hand sanitiser, but when soap and water aren't available, sanitiser is an effective alternative.
  • Hand sanitiser should be 60 to 95 percent alcohol to be effective at protecting you against infectious disease.
  • This article was medically reviewed by Graham Snyder, MD, MS, who is the medical director for the Infection Prevention and Hospital Epidemiology branch at University of Pittsburgh Medical Center.
  • Visit Business Insider's homepage for more stories.

Hand soap and hand sanitiser might seem interchangeable, but they are meant for different circumstances. While sanitiser is smart to have on hand for when you are on the go, healthcare professionals agree that nothing beats a thorough hand wash with regular soap and water. To learn how and when to use hand sanitiser and understand why experts prefer soap and water, Insider spoke to Alex Berezow, microbiologist and Vice President of Scientific Communications at the American Council on Science and Health.

The effectiveness of hand sanitiser

The main ingredient in most hand sanitisers is isopropanol (rubbing alcohol) or ethanol (the principle ingredient in alcoholic drinks). Alcohols have a long history of being an effective disinfectant against some viruses and bacteria, as long as the solution has the right percentage of alcohol.

Hand sanitiser is a practical backup if you don't have access to soap and running water. But in general, sanitisers aren't as effective as hand washing, plus they require proper technique and diligence to work properly.

"People generally don't use enough volume of hand sanitiser or spread it around their hands as far as they should," says Berezow. The proper application of hand sanitiser is essential to its effectiveness. To use hand sanitiser correctly, apply the specified amount as directed by the product's label to the palm of one hand, and rub the sanitiser thoroughly over both hands until they feel dry. The CDC advises that this process, much like hand washing, should take 20 seconds.

Hand sanitiser is efficient at killing some microbes, but not all of them. Here are some germs that it can't protect you against:

  • Cryptosporidium . A parasitic infection that cause breathing and gastrointestinal issues.
  • Norovirus. A viral infection that can cause vomiting and diarrhea.
  • Clostridium difficile . A bacterial infection that can cause intestinal upset and inflammation

What to look for in hand sanitiser

Alcohol-based sanitisers should contain at least 60 percent alcohol. Preferably a concentration ratio between 60 to 95 percent is best. Anything lower than that and you aren't doing much good. According to the CDC, sanitisers with less than 60 percent alcohol just reduce the growth of germs rather than eradicate them completely

Beware of hand sanitisers with too little alcohol, or hand sanitisers that use alcohol substitutes, which are not as effective or recommended by the CDC. The prolific use of hand sanitisers also comes with drawbacks. "Using too much hand sanitiser dries your hands out, and they can crack and bleed. If you have a skin condition like eczema, this could exacerbate it," says Berezow.

Alcohol-based sanitisers can also cause alcohol poisoning if more than a couple of mouthfuls are swallowed, so be sure to store any hand sanitiser out of reach of children.

Why soap and water is better than hand sanitiser

Although using hand sanitiser is better than nothing, the CDC and other health experts say that soap and water is the best way to practice good hand hygiene and protect yourself.

While hand sanitiser may kill germs, it doesn't do anything to physically remove germs from your skin like soap and water do. "Soap is a detergent, which is why it gets all sudsy and bubbly. Detergents work by dissolving both water and oil, so it simply washes the microbes off your hands like it would wash the grease off a dinner plate," says Berezow.

The CDC says that hand washing, while it doesn't directly kill germs, reduces the number of germs on your hands. Soap and water are more effective than hand sanitisers, especially when your hands are visibly greasy or dirty. After eating, playing sports, if your hands are soiled and greasy, then hand sanitisers aren't as effective.

The CDC recommends that you wet your hands with running water, turn off the tap, and then scrub your hands with soap for at least 20 seconds. If you don't wash for at least 20 seconds, it makes a huge difference. Here's a look at some different washing methods and times to give you an idea of how much cleaner a thorough 20-30-second scrubbing provides.

Using soap is much more effective than hand sanitiser because the soap contains surfactants, which are substances that lift oil and microbes from the skin. Keep in mind that there is no difference between using plain soap and using "antibacterial" soap, as they are both proven to have the same effectiveness.

After you have lathered with soap, rinse your hands under clean running water and then immediately wipe them with a clean towel. Since germs can be transferred more easily to and from wet hands, it is important that you dry your hands as soon as you finish rinsing them. Soap and water will effectively prevent the spread of viruses and bacteria, but it will do no good against a current infection. However, washing your hands will help you prevent spreading your illness to other people.

The bottom line

Berezow makes it clear, "soap is a detergent that washes away the microbes, while alcohol in the hand sanitiser directly kills microbes. But soap and water are most effective at removing the microbes." The microbes alcohol-based sanitisers cannot kill will be washed away with proper handwashing.

The CDC recommends using an alcohol-based hand sanitiser of a 60 percent and up concentration only when soap and water are not available.

If your hands are soiled, find access to running water and soap as soon as possible as hand sanitiser may not be very useful when dirt and grease are present.

So, clean soap and water are still the best defense against germs. Wash your hands anytime you are preparing or eating food, after you use the bathroom or change a diaper, after blowing your nose, touching an animal, or the garbage. Take special care if you are looking after someone who is sick to help prevent spreading the illness.

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