Hair is a fibre. Treat it like one.

A hair is a dead protein fibre with a scale structure on the outside and a cortex inside, which is a technically precise description of a strand of wool. It responds to heat, water, friction and chemistry exactly as any other keratin fibre does. Once that is accepted, most of the confusion in hair care resolves, and so does most of the spending.

The cuticle, which is the whole game

The outer layer is a set of overlapping scales lying towards the tip. When they are flat, light reflects evenly and the hair looks glossy and slides against itself. When they are lifted, by alkaline products, by heat, by rough handling, the fibre catches on its neighbours, tangles, looks dull and loses water from the cortex underneath.

Almost every worthwhile product does one of two things: keeps the scales flat, or temporarily fills the gaps where they have been lost. Nothing regrows them. The word repair on a bottle means a cosmetic filling that survives until the next wash, which is a legitimate thing to buy as long as you know what is being sold.

Wet hair is weak hair

Keratin swells with water and loses roughly a third of its tensile strength. That makes the brush immediately after a shower the single most damaging tool in most bathrooms. Detangle before washing, and if hair must be handled wet, work from the ends upward with a wide tooth comb and no tension.

The same physics explains why hair dries into whatever shape it is held in, and why sleeping on wet hair produces both a shape you did not want and mechanical damage along the friction line of the pillow. A silk or satin pillowcase is not a luxury indulgence here, it is a lower friction surface, and the effect on breakage is measurable.

Heat, and the number that matters

• Keratin begins to change permanently above about 180 degrees. Most straighteners run to 230.
• One pass at 180 does less damage than three passes at 150, because dwell time compounds.
• A heat protectant is a thermal buffer, not a shield. It buys perhaps 20 degrees of headroom, not permission to use 230.
• Blow drying at medium heat, moving constantly, held a hand span away, from eighty per cent dry rather than soaking, is far gentler than the alternative of going to bed wet.

Damage is cumulative and hair grows a centimetre a month. What you do to it today is still on your head in two years.

Washing, and the frequency argument

Shampoo removes sebum, which is the fibre natural conditioner, so the honest frequency is as often as the scalp needs and no more. That is genuinely daily for some scalps and twice weekly for others, and the difference is scalp oil production rather than virtue. The compromise that works for most: wash the scalp, condition the lengths, and never the reverse.

Sulphate free is not automatically gentler, since some sulphate free surfactants are harsher than a well formulated sulphate, but it does tend to be less stripping on colour treated hair. Silicones are not the villain either, they are smoothing agents that build up if the shampoo cannot remove them, which is an argument for matching the pair rather than for avoiding a chemical class.

What money buys, and where it stops

Above about twenty five for a shampoo the formulation gains are small and the sensory gains are real. Where money does buy performance is in bond building treatments, which genuinely reconnect broken disulphide bonds after chemical processing, and in a good cut, which removes the damage you cannot fix and is the only true repair in the category.

Spotted an error? Tell the desk