What it is: L’Oréal Paris Advanced Haircare Total Repair 5 Damage-Erasing Balm, $6.99What it does: Transforms hair damaged by heat styling, chemical treatments or the environment. Softens rough ends, tames flyaways and infuses shine.Why it works: The treatment touts arginine-k complex as its main source of damage control (arginine is one of the main components of keratin, a popular—and effective—smoothing protein). It coats your hair follicle with a strengthening reinforcement layer. Also cool about the formula is how it was tested for efficacy: To make sure it was sufficiently penetrating the hair’s core, L’Oréal used X-ray Tomography—a technology borrowed from nuclear physics—to look inside hair fibers.Why you care: Ninety-five percent of women think their hair lacks softness or is brittle, according to the nearly 40,000 women who have taken our Hair Age Quiz. This will help repair your fibers and reverse some of the damage that’s giving your hair its dry, dull texture.QUIZ: How Old Does Your Hair Look?