Q: Is there any difference between washing our hands with bar soap or liquid hand wash? Would it be better if we wash with both soap and hand wash at the same time? — Rowena Kong, Vancouver, Canada
A: The debate over whether bar or liquid is best has been ongoing for decades, but a 2006 study nearly put an end to bar soap’s clean credentials. It found that the more consistently wet the bar soaps were and the more they were used, the more potentially harmful microbes they hosted.
Counterintuitively, this is because of how soap works: When it mixes with water, the soap’s fats break down and lather, increasing the solubility of what’s on your skin, including bacteria. But water alone can’t remove all bacteria, and since some water remains on the soap’s surface after you’ve finished washing, some bacteria lingers in that water.
Luckily, soap is water soluble, so just rinsing the bar reduces bacteria on it. And there’s nothing wrong with using it at home, where presumably fewer people (and their germs) will touch it. Still, the Centers for Disease Control and Prevention recommends people use liquid hand wash to minimize the risk of spreading harmful bacteria. Even though refilling liquid hand wash dispensers can turn them into potential havens for microbes, liquid still trumps bar in the CDC’s eyes. That’s because people can either dispose of the dispensers or thoroughly clean them before refilling, decreasing the chance they’ll harbor bacteria.
As for mixing the two, CDC spokeswoman Brittany Behm says, “We don’t think there is any reason to use both bar and liquid soap simultaneously.” So stick to the soap you like best.