Dry, chapped lips are painful, unattractive and can happen all year round — and sometimes, your standard lip balm just doesn’t cut it. That’s where a lip serum, also known as a lip treatment, comes in: a hydrating treatment that helps relieve severely dry lips and allows you to wear your favorite lipstick or liner without worrying about cracks and flakes. To narrow down the best lip serums to shop, we put dozens to the test during the brutal northeast winter (which conveniently included several