From styling treatments to straightening complexes and deep conditioners, it seems the great keratin tide has swept over every hair product category on the market today.With the protein appearing in such a diverse range of items, it can be confusing to decipher what exactly it is that keratin does, and for which hair type it’s best suited. For instance, are keratin-branded hair care products just for those who have had keratin-containing treatments? And some consumers are even concerned about the ingredient’s safety, since it’s found in countless straightener formulas containing controversial actives, like formaldehyde, that can damage hair.MORE: BB Cream For… Your Hair?Experts say that you can relax: Keratin has been around for a long time, and its function is only one of protection. “Keratin reinforces your hair,” YouBeauty Cosmetic Chemistry Expert Ni’Kita Wilson. “It’s a protein that forms a film on hair strands, creating a scaffolding-like structure that’s suitable for all hair types,” she adds.So whether fine, thick, normal or chemically-treated, your hair can benefit from the temporary barrier keratin creates between strands and your environment. It’s the other ingredients in the formula that determine whether or not a product will work best for you.MORE: Get The Facts About Color-Safe ShampooAt the drugstore, keratin is taking center stage in a spate of new launches. Pantene Advanced Keratin Repair Split End Fuser and 60 Second Therapy Ampoules (each $14.99) are both highly concentrated treatments that focus on frayed strands and dryness. Tresemmé has incorporated the protein into its Keratin Smooth Shampoo, Smoothing Serum and Heat Protection Spray ($5-$10) to specifically target damage-induced frizz for a sleeker finish.In prestige boutiques, keratin is joining more elegant ingredients. AG Reconstruct Intense Anti-Breakage Mask ($24) blends silk proteins and shea butter with keratin and panthenol to intensely hydrate hair in need of reconstruction. KeratinPerfect 30-Day Brazilian Hair Smoothing System Essentials Collection ($95) houses two shampoos, a conditioner, smoothing treatments and a daily spray that fuses the protein to rough spots where natural keratin has been depleted for a faster blowdry and style. Meanwhile, Phyto has cleverly added hydrolyzed keratin to Phytovolume Actif Maximizing Volume Spray ($28) for fine, limp hair to physically build girth and texture around strands.QUIZ: How Healthy Does Your Hair Look?Keratin is one trend that doesn’t seem to be fading anytime soon—but count this as one of the rare crazes that’s totally worth the hype.