Damaged hair — whether that's from overstyling or bleaching — tends to loose its natural shine and luminosity, and that's because the cuticle (i.e. the protective layer around each individual strand) is all messed up. The cuticle is made up of overlapping cells that point downwards — like fish scales or roof tiles. When those tiles lay smooth and flat, they refract light in a way that makes your hair shampoo-ad levels of shiny. When those tiles are damaged and pointing in all directions, then they don't refract light as well and hair ends up looking lacklustre.
The Inkey List Vitamin C Brightening Hair Treatment (£10), which is silicone-free like all the products in the range, uses a combination of vitamin C and an active compound called Lustreplex to help flatten the cuticle. "It all has to do with the refraction of light, and when the cuticle is flattened, the light shining off of the hair will be much brighter," explains Curry.