As keratin becomes more commonplace in hair formulas, it’s important to learn what it actually is—and does

Keratin has been a hot-button word the last several years as various straightening treatments came onto the market to great controversy. While formaldehyde marred some formulations, keratin is actually just “a strong protein that is a major component of hair, nails and skin,” says Doreen Guarneri, co-creator of Pure NV BKT (Nature’s Vitamins, Botanical Keratin Treatments) from American Culture. “Approximately 50 percent of human hair is composed of keratin. But when hair is damaged due to chemical treatments, excessive hair styling or other environmental factors, keratin breaks down. Aging also depletes it.” Think collagen’s role in the skin, keeping it plump, healthy and youthful.

Guarneri, whose sulfate-, sodium chloride- and paraben-free product line ranges from shampoos and conditioners to healing styling products and a repairing mask, says the role of keratin in so many formulas these days—and it’s in many, from KeratinPerfect’s sizable collection to Phyto’s hyaluronic acid-tinged Phytokeratine Reparative Conditioning Treatment—is “rebuilding hair fiber on damaged hair by bonding to it, replacing the proteins that are lost. Depleted keratin in the hair [is like] potholes in the road—it causes damage to the external layer, creating holes in the cuticle and frizzy, dry, brittle, unmanageable and overall unhealthy hair,” says the hair guru.

Fortunately, that damage is reversible. “Replacing the lost keratin fills in the holes, creating an even surface on the hair—much like a newly paved road—restructuring and reconditioning hair fibers to restore health and vibrancy while adding incredible shine.” And contrary to common belief, this wonder-working protein does not straighten hair. “It makes hair smooth with a frizz-free finish. It’s absolutely beneficial for curly hair, as it tends to be keratin-deprived by nature,” says Guarneri. “Using keratin-based products will [give] smooth, healthy, bouncy results.”

And just as with anything, moderation truly is key. It is actually possible for someone to use too much keratin, “over-protein-izing the hair,” she says, and making it brittle and hard. Pure NV BKT was formulated to prevent this with fatty acid-rich argan oil and botanicals like pomegranate and eggplant that balance out the hydrolyzed keratin and also fight against aging and encourage good scalp health. So while a child doesn’t need it, any mane that’s been “compromised by chemical services, aging or wear and tear will highly benefit from keratin.” The results are cumulative. “The more keratin you replace in your hair, the better condition it will be in.”