You can’t rebuild a strand of hair”: what an expert reveals about damaged hair
You’ve tried mask after mask and repair treatment after repair treatment, yet your lengths stay dull, brittle, or lifeless. The problem may not be a lack of care, it may be that you’re targeting the wrong thing entirely. Understanding what actually weakens damaged hair changes everything about how you treat it.
What’s really happening inside the hair fibre
Before reaching for a product, it helps to understand what’s breaking down. The cuticle, that protective outer layer made of overlapping scales, plays a central role. When it lifts under the effect of colouring, bleaching, chlorine, or sun exposure, moisture escapes more easily and the cortex, made up of keratin fibres, is left exposed.
Olivier Lebrun, founder of the brand Blown, frames the question differently. For him, it’s not the technology behind a treatment that matters most, but the precise need of the hair itself. He points out that the fibre is the same material regardless of hair type, what changes is where it gives way and why.
His conviction is clear: you cannot rebuild damaged hair. What you can do is restore a healthy appearance, give it back cohesion and resilience to styling, by supplying molecules close to those the hair produces naturally. The right question, then, is not which technique to apply, but what exactly the fibre is missing.
Matching the treatment to each type of damaged hair
Fine hair: beware of overloading
With fine, weakened hair, the most common trap is trying to over-nourish it. According to Olivier Lebrun, fine hair breaks because it has little reserve, and because we often weigh it down with formulas that are too rich. In his view, the texture of a treatment accounts for almost half the result.
Repair mists and lightweight milks are the way to go, provided they absorb without leaving too much residue. Light botanical oils can round out the routine. Heavy, thick textures, on the other hand, risk flattening volume and amplifying that weighed-down feeling.
Curly and textured hair: structural dryness
Curly hair is naturally dry. It tolerates, and even calls for, rich, melting textures loaded with lipids. Shea butter masks, botanical oils, and certain amino acids can all earn a place in the routine.
Sébastien Thibaut, head of advanced hair research at L’Oréal, adds further context. Textured hair is among the most fragile, as it has fewer cuticle layers. On top of that, every spiral creates an additional point of weakness. And its sebum, which is waxier, doesn’t travel down the length of the strand, so it never naturally lubricates the fibre.
Straight hair: loss of shine above all
When the cuticle of straight hair is damaged, the surface becomes less smooth and reflects light less effectively, leaving the hair looking dull. Water also penetrates the fibre quickly before escaping just as fast, which can encourage frizz.
Treatments containing keratin, ceramides, or botanical oils help improve the look of the fibre and smooth the scales back down. The goal is to choose a formula suited to the hair’s current condition, without piling on products.
The special case of colour-treated hair
Colouring and bleaching damage hair in a very specific way. Olivier Lebrun explains that these processes deliberately open the cuticle to allow pigment in or out, which alters the structure at a deep level. The fibre becomes porous, loses its proteins, and can no longer retain moisture properly. The hair’s pH is also disrupted after colouring, creating an additional imbalance.
In this context, he recommends a slightly acidic treatment capable of tightening the scales back down. Sébastien Thibaut highlights citric acid, whose small molecular size allows it to penetrate to the core of the fibre and re-form damaged bonds. The routine can also incorporate antioxidants, UV filters, and heat protection. For heavily sensitised hair, bonding treatments aim to reinforce certain bonds and improve the fibre’s overall resilience.
Porosity and everyday habits to limit breakage
Hair type alone doesn’t always point you toward the right treatment. Hair porosity gives a valuable indication of the fibre’s ability to retain water and active ingredients. Three at-home tests can help assess it: the glass of water test, the finger test, and the water spray test. They reveal the condition of the cuticle scales and help you adapt your product textures accordingly.
Low porosity hair does better with light, water-based formulas. High porosity hair, on the other hand, benefits from more proteins and fatty substances to help lock moisture into the fibre. With a consistent, progressive routine, visible results can appear within 4 to 6 weeks: more radiance, better shine, less frizz, and less breakage.
Products, however, can only do so much. Here are the practical habits to adopt to protect your lengths day to day:
- Limit the use of heat-styling tools
- Apply a heat protectant before any exposure to heat
- Avoid vigorously brushing wet hair
- Choose hair ties that don’t put excessive pressure on the fibre
- Trim severely damaged or split ends, as no treatment can permanently repair a split end
On that last point, cutting remains the most effective way to remove the most damaged sections. Treatments can improve the appearance of split ends, but they don’t seal them shut for good. The best approach is to combine a solid routine with regular trims to keep the fibre healthy from root to tip.
