Worth being clear about what this is for before you buy it. Aminexil is L'Oreal's patented molecule aimed at hair fall caused by weak, breaking strands, not at hereditary hair loss. If your hair is snapping mid-length, coming out on the brush after colouring or heat styling, or thinning from stress and poor condition, this is the right product. If you are losing hair at the temples or crown in a receding pattern, no cosmetic serum will change that, and you want a dermatologist instead.

For breakage-driven fall the formula is a serious one. It carries 1.5% Aminexil, which L'Oreal states is clinically proven to strengthen hair and reduce hair fall by up to 92%. Caffeine and arginine sit alongside it, both aimed at the scalp rather than the hair shaft, which is where this kind of treatment has to work.

It goes onto the scalp, not through the lengths, and it is a leave-in. Do not rinse it out. That trips people up on the first use and it is the main reason a serum like this gets written off as ineffective.

Suits: hair prone to breakage, post-colour or post-heat damage, and anyone seeing more hair than usual on the brush. Works on wet or dry hair.

Worth knowing: L'Oreal recommends running it as a six-week course with daily use, and results on any hair treatment are slow by nature since hair grows about a centimetre a month. The dose is marked on the side of the bottle. Be realistic about the timeline and it will not disappoint you.