Two different problems
Hair and scalp get treated as one subject because one product usually addresses both, which is a commercial convenience and not a physiological fact.
Hair is dead. It is a keratin fibre with an outer cuticle of overlapping scales lying like roof tiles, a cortex beneath and, in thicker hairs, a core. Once it has left the follicle nothing repairs it. Everything that happens to hair is either physical damage to that structure or a coating applied over it.
Scalp is skin. It has a stratum corneum, sebaceous glands attached to follicles, its own resident population and its own microclimate under hair. Everything in the rest of this publication applies to it, plus a few things that do not apply anywhere else.
What salt water does to hair
The cuticle scales lie flat on healthy hair, which is what makes it feel smooth and reflect light.
Water swells the fibre, which lifts the scales. Salt crystals forming as the water evaporates sit between and under lifted scales. Mechanical handling of hair in that state, combing it wet, towelling it hard, dragging a hood over it, chips and lifts scales further.
The result is a fibre with a rough surface, which is why sea hair tangles, why it feels dry when it is not chemically dry, and why it looks dull. The scales do not grow back. What happens instead is that the damaged length is eventually cut off.
The controls are the ones that follow from that: rinse the salt out with fresh water before it dries, do not comb hard while wet, blot rather than rub, and put a hood on hair that is not full of crystals.
What happens to the scalp
The scalp has three things going on that other sites do not.
It has its own lipid supply. Sebaceous glands attached to follicles produce sebum, and the scalp is one of the densest sites for them. This means the scalp is generally better protected than facial skin and worse suited to aggressive washing.
It is rarely rinsed properly. Salt that lands on a face gets rinsed. Salt in hair does not, because rinsing hair takes longer and people are cold. It then sits on the scalp for hours, drawing water from a surface that already has a hood over it.
It spends the session under the least ventilated item of kit. A hood is occlusion applied to a site that is warm, has hair on it, and is usually the last thing rinsed and dried after a session.
| Hair | Scalp | |
|---|---|---|
| What it is | Dead keratin fibre with a cuticle of overlapping scales | Skin, with a dense sebaceous supply |
| Can it repair itself | No, ever | Yes, on the ordinary epidermal timescale |
| What salt does | Crystals under lifted scales, then mechanical chipping | A drawing film left in place for hours |
| What the hood does | Drags over lifted scales | Occlusion, warmth and an unrinsed surface |
| What actually helps | Rinse before drying, handle gently when wet | Rinse thoroughly, wash less often, wash the hood |
Ordering framework written by this publication from general skin physiology. It is not a measurement, it is not taken from any study, and no number in it is a reading.
Flaking and itch
This is where we need to be careful, because scalp flaking and itch have several possible explanations and most of them are conditions we do not discuss.
What we will describe is the environmental contribution. A scalp that is left with salt on it, held under an unrinsed hood, and then washed aggressively with a strong detergent to compensate, is a scalp with a disrupted barrier and a raised surface pH. That will flake and itch on ordinary physical grounds.
What we are not going to do is tell you that your flaking is that, because scalp flaking is also a presenting feature of several recognised conditions that require assessment. If flaking is persistent, if it is greasy and yellowish, if there are defined scaly patches, if there is redness beyond flaking, if it itches enough to disturb sleep, or if hair is coming out with it, that is a pharmacist or GP matter and not a website matter.
The washing question
People who are in the sea several times a week face a genuine dilemma. Salt must come out, and washing the scalp repeatedly with a strong detergent is its own insult.
The resolution follows the same logic as everywhere else on this site. Salt is soluble. Fresh water removes it. A thorough fresh water rinse, taking the time to actually get it to the scalp rather than the surface of the hair, achieves most of what is needed without detergent.
Reserve the detergent wash for when the scalp genuinely needs degreasing rather than for every session. That is a change in frequency, which is the variable that matters, rather than a change in product, which mostly is not.
The hood
One specific piece of advice, because it accounts for a surprising share of winter scalp complaints.
A hood is worn tight against the scalp, forehead, ears and neck. It is warm and wet throughout the session. It is the item least likely to be rinsed and dried, because it is small and gets put in a bag.
Rinse it, dry it, and if a recurring scalp or hairline complaint appears in the same place each winter, the hood is the first thing to suspect. Marks along the hairline and behind the ears are almost always the hood, and they are mechanical, which is why they respond to fit and to rinsing rather than to shampoo.