Everything you need to know about hair serums.

Hair serum is a concentrated treatment formulated to address specific needs, whether along the hair lengths or on the scalp.

Unlike a conditioner or a mask, it does not rinse out : hair serum remains, in the vast majority of cases, applied to deliver a sustained effect. The formulations are typically lightweight, often aqueous when formulated for the scalp, and occasionally richer and more oily when targeting the hair fiber. This diversity of textures mirrors the wide range of applications for hair serums : to soothe an irritated scalp, to rebalance excessive sebum production, to strengthen the roots, to smooth cuticle layers, to protect split ends, or to enhance shine.

We distinguish two major families of hair serums : those applied to the scalp and those designed for lengths and ends. Each category encompasses several subtypes, depending on the targeted concerns.

Scalp serums.

With regard to the scalp, several serums are available. The anti-dandruff serums often combine mild keratolytic active ingredients, such as salicylic acid, with antifungal agents, such as ciclopirox olamine or piroctone olamine. They are generally used alongside anti-dandruff shampoos and for maintenance, to prevent relapse.

There are also hair growth serums, sometimes referred to as hair regrowth serums or anti-hair-loss serums. Despite these different labels, they are equivalent products. They typically contain actives that enhance blood circulation, such as caffeine, to optimize nutrient and oxygen delivery to the hair bulbs, and ingredients that reinforce follicular anchoring, such as specific peptides. That said, while these serums may help to some extent to stimulate the hair growth, their effects remain more limited compared to medico-aesthetic treatments like PRP (platelet-rich plasma). Moreover, no method can accelerate the rate of hair growth beyond the limits set by genetics.

Finally, the rebalancing serums for oily scalps rely on purifying and mattifying ingredients to limit excessive sebum production by the sebaceous glands, while avoiding stripping the skin to prevent rebound effects. In practice, these formulas often combine sebum-regulating agents, such as zinc or niacinamide, along with soothing actives that reduce inflammations related to hyperseborrhea. The goal is to restore a healthy scalp that does not become oily too quickly.

Serums for hair lengths.

As for serums formulated for the hair lengths, they are primarily designed to improve the appearance and strength of the hair fiber. Notably, there are hydrating serums, which add flexibility by reducing water loss, and fortifying serums that reinforce the cuticle to minimize breakage. In practice, these two functions are closely linked, which is why many products claim both moisturizing and protective benefits.

Most of these hair serums also target frizz : they contain film-forming agents, such as polymers, which smooth the cuticle surface and prevent moisture from penetrating the fiber responsible for uneven hair swelling. Some are even marketed as smoothing serums, which is somewhat misleading. In reality, these treatments do not alter the hair's natural shape but help to control the fiber. Only a heated tool can produce a straightening effect at home. Some are also offered with heat-protective serums designed to protect the hair fibers from high temperatures.