From sharing earbuds with your best friend to listen in on a movie, or borrowing some from a co-worker to zone out at work, using someone else's earbuds seems innocent enough, right? Nope! Before we get into specifics, let's state the facts: Earwax is our body's natural way of protecting the insides of our ears and preventing infections. And, yes, that wax has bacteria on it, but it's pretty harmless. Enter earphones, which trap the bacteria (and any germs on the earphones already) in the warm, dark environment of your inner ear. That once innocent earwax can build up on those earphones, "acting as a layer to trap bacteria and prevent it from drying out so it can survive and grow," says Kelly Reynolds, PhD, associate professor of environmental health at the University of Arizona, to Buzzfeed. (Here's what your earwax says about your health.) "If these bacteria become too numerous, it can lead to infections," says Dr. Abbas Anwar, MD, an otolaryngologist at Southern California Head & Neck Medical Group in Santa Monica, California. "Also, earbuds can sometimes cause small abrasions and cuts within the ear canal, especially if they are worn for long periods of time or while sleeping/exercising. These cuts can serve as a portal of entry for bacteria and lead to painful outer ear infections (otitis externa)." Now, if these are the consequences of overusing your own headphones, imagine the results of using someone else's. "You are introducing new and more numerous amounts of bacteria into your ear," says Dr. Anwar. "In addition, you probably don't know if your friend has been keeping their earbuds clean. They can pick up all sorts of bacteria from different surfaces such as tables and purses, and these new 'foreign' bacteria can lead to infections in your ear." (If you do end up getting an ear infection, here are some home remedies to cure it.) Besides not sharing earbuds, there are plenty of ways to make sure your own are clean and safe for your ears. Purchasing individual cases for your earbuds, regularly wiping them down with alcohol, and keeping them dry are excellent ways to keep your ears clean and infection-free.