Wing Hong Seto, co-director of the WHO’s Collaborating Center for Infectious Disease Epidemiology and Control, set the record straight in a video interview for Bloomberg. He flatly stated that wearing the blue side out is the only way to wear a mask correctly, and referred to wearing a mask white side out as “totally wrong.” Medical masks are proven to be effective, he explained, but not if you wear them inside out. There is, however, one thing that the viral post got right. The two sides of the mask do serve different functions: the blue side, Seto explained, is waterproof, and designed to protect the wearer from incoming droplets from others. The white side, on the other hand, is absorbent. “So, if I cough, it absorbs it,” Seto noted.ae0fcc31ae342fd3a1346ebb1f342fcb The key, he explains, is to trap your own germs while repelling the germs of others. Reversing the mask can have the opposite effect, dangerously trapping the germs of others on the outer surface of your mask, and increasing your likelihood of contamination. RELATED: For more up-to-date information, sign up for our daily newsletter. So, if you’ve been wearing a blue mask to keep yourself and others safe from coronavirus, make sure it’s on properly—meaning always blue side out. And if you’re wondering how long masks will be a part of daily life, check out Here’s How Long You’ll Have to Wear a Face Mask, Experts Say.