Nexxus Curl Define Line Adds Protein Without Making Natural Hair Brittle | Review

Hard, brittle, unyielding — these aren’t adjectives you want to describe your hair. But the first time I used a protein treatment in the hopes of strengthening my 4B curls, they hardened into a helmet. It was probably because the formula’s keratin proteins sat on top of my hair instead of penetrating it, says Fraser Bell, Nexxus’s science insights leader. Bell and his team took 10 years to come up with an alternative solution, a range of protein products tailored to naturally curly hair: Nexxus Curl Define range. 

Generally, I turn to a protein treatment when I notice extra breakage around my hairline from too many slicked-back Afro puffs, or there is extra shed hair in my trash can after the detangling process. Curly hair is inherently fragile. “Very, very curly hair is particularly prone to breakage [because you] have all these natural twists and turns in the fiber,” says Bell. “When you extend a fiber with lots of natural twists and turns, you get lots of concentrations of stress, and the fiber can fail where these high stress concentrations are.” Regular wash-day steps like detangling and twisting, which pull the fiber straight, can can curls to snap.

“Proteins can fill in gaps in damaged hair strands,” says cosmetic chemist Ni’Kita Wilson. “This [shores] up weak spots and reduces porosity to help control the flow of water in and out of the strands.”

So, it seem counterintuitive, but a good balance of protein can help keep hair moisturized… if it’s done right. But until I tried the Nexxus Curl Define line, I didn’t think protein products could leave my hair actually feeling soft.

Nexxus scientists began studying the structure of hair on a molecular level: They discovered that curly hair contains more proteins that are rich in two particular amino acids — glycine and serine — than straight hair. So curls are better treated by silk proteins (which are naturally high in glycine and serine) than the keratin proteins you typically find in hair care.

This research has culminated in Nexxus Curl Define, a line of shampoo, conditioner, and treatment products. Every formula is infused with silk protein, whose amino acids work their way inside the core of curly hair. Bell and his team made sure that the line strikes the right balance because while some hair types need lots of protein to replenish keratin that is naturally lost during heat-styling, natural hair tends to be manipulated much less.