Response: The common cold is caused by a viral infection of the respiratory tract that produces runny nose, sneezing, congestion, and other symptoms. In laboratory tests, alcohol-based hand sanitizers like Purell have been shown to inactivate viruses and make them non-infectious. To be effective, however, the sanitizer has to get to the virus before the virus reaches your nose and begins an infection that leads to a head or chest cold.
There are many types of viruses that can cause an infection that can result in a head or chest cold. You can come into contact with any of these viruses by two routes, by breathing them in through your nose or mouth or by touching the virus and then your nose or mouth with your hands. As you might expect, hand sanitizers work best against viruses that are transferred by your hands rather than through the air. Scientific studies conducted to date show that head and chest colds happen less frequently (by about 15%) when alcohol-based hand sanitizers are used in schools, day care facilities, and nursing homes. These same benefits, however, have not been shown in homes in the United States. Despite this, you may still want to use alcohol-based hand sanitizers in your home, as they have been shown in the same studies to reduce the spread of "stomach bug" infections that cause diarrhea and upset stomachs by more than 50%.
Regardless, it makes sense to reduce your exposure to viruses and other infectious agents that can cause head or chest colds. Using alcohol-based hand sanitizers seem to be a relatively effective way to do so, and given their ease of use and relative low cost, they may be a good -- if only precautionary -- way for you to reduce your risk of getting a cold. Of course, there are other effective and easy ways to reduce your chance of getting a cold, including hand washing with soap and water, flu shots, and washing toys and other items that are shared among small children.
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Helen Suh MacIntosh is a professor in environmental health at Harvard University and studies how pollution behaves in the environment and how it affects people's health. Please keep in mind that her answers are just her interpretation of available information and should not be taken as the only viewpoint or solution to a problem. Use this column at your own risk. Having said this, please feel free to post any of your environmental health questions to Helen@TreeHugger.com (please use a descriptive email subject line and mention if you want to remain anonymous or not).