"Hair serum is usually seen as a finishing product," says Peter, "but it works well when applied before you wash your hair. Take a few drops in your hands, coat the surface and simply run it through. Some of the product will come out in the wash, but a lot of it doesn’t, and what isn't washed away stays within the cracks and smooths the hair surface. This adds a level of protection to the hair when you’re washing. I liken the hair strand to a scratched table. When you’re repairing it, you pile on the polish but you remove 99% of it, and what’s left plugs the gaps and leaves you with a nice polished surface."