Hand sanitizer is a daily staple for parents on diaper duty, commuters who hold those rarely-cleaned handle bars on buses and subways, and many other people in between. In fact, according to global information company NPD Group, hand sanitizer sales in the United States shot up 37 percent from 2017 to 2018 alone. And while it’s perfectly fine to turn to this bottled product as a last resort, you shouldn’t opt for hand sanitizer over washing your hands in the sink if there’s clean water and soap available to you.

As it turns out, there’s a reason why most hand sanitizer companies don’t claim to kill 100 percent of germs and bacteria: Because they don’t. Some of the viruses and germs you’re leaving on your hands every time you opt for hand sanitizer instead of soap and water.

According to the Centers for Disease Control and Prevention (CDC), norovirus is a “very contagious virus” that can be spread via direct contact, contaminated food or drinks, and contaminated surfaces. And while thoroughly washing your hands (and your produce) is a good way to ensure your safety, using alcohol-based hand sanitizer isn’t quite as effective.

In one 2011 study published in the American Journal of Infection Control, researchers analyzed data from health departments in three states and found that the facilities that relied on hand sanitizer were more likely to experience a norovirus outbreak than those that favored hand-washing.