Sometimes the contents of your BFF’s make-up bag are way more exciting than your own, and you’ve never met a tester product at Sephora that you didn’t want to immediately put on your face. But proceed with caution. Here’s what can happen when you share beauty products. You can get cold sores – keep your friends close, and your lipstick collection closer. “Herpes simplex virus AKA perioral fever blisters (and) cold sores can be transmitted via the oral secretions left behind on lip liners, lipsticks, lip glosses, and stains,” warns Elizabeth Donat, a licensed aesthetician and the owner of EMD Skin Solutions. “In my years of working at the beauty counters, I have seen customers, random children, and employees apply testers directly to their lips, creating unsanitary conditions and possible health hazards. You don’t want an innocent application of lipstick to result in a lifelong, contagious skin condition – it’s not worth it!” You can get sick – sharing lip products can also mean more sick days. “Whether you have a roller-ball, squeeze tube, or sponge-tipped applicator type, viruses and bacteria from your mouth can transfer right back into the tube, making it a way to spread cold and flu viruses,” says Tsippora Shainhouse, MD, FAAD, a dermatologist in Beverly Hills, California and a clinical instructor at the University of Southern California. Watch those tins of lip balm, too, she adds. “Dipping dirty fingers carry bacteria from the environment and transfer them into the pot. Transferring them to your mouth can give you a rash or make you sick.” You risk getting pink eye – “Conjunctivitis is one of the most common infections that can be transmitted via unclean eye make-up, and it is highly contagious,” says Donat. “Unless you are dipping into these products with clean, single-use applicators like q-tips, wooden sticks or plastic spatulas, and/or sharpening pencils after each use and wiping them with alcohol, these items cannot be sanitised.” You end up sharing eye yeast and bacteria – seriously, keep your friends’ make-up out of your eyes. “Goopy mascara in its dark, closed tube is exposed to germs every time the wand is dipped back into it,” says Dr Shainhouse. “Eyelids and lashes can carry yeast, bacteria, and viruses that can grow in that tube and be transferred to the next user.” You can break out – when it comes to make-up sponges like the beauty blender, Donat says the jury’s out on the best way to sanitise them. “Spongey, damp materials like beauty blenders are the perfect environment for bacteria to grow and fester, so keep them to yourself and toss them often, especially if you are breakout-prone.” You may want to keep your makeup brushes to yourself, too – unless you’re bothering to thoroughly shampoo them, rinse them, and leave them to dry overnight between uses, which is the only sanitary way to use makeup brushes on different people, according to Donat. You swap dead skin cells and oils – it can be tempting to share expensive cleansing devices like the Clarisonic with someone else, but don’t do it, says Donat. “Cleansing brushes are fantastic for getting makeup, sebum, bacteria, and dead cells off the skin, but are not meant for sharing.” Think about how good those brushes are at removing nasty gunk from your friend’s face – and think about that stuff living on a cleansing brush without proper cleaning, then putting it right back on your face after she uses it. Ew. Donat says, “You wouldn’t share your toothbrush with anyone, would you?”