KeraCoconut oil for hair, and the oils that only sit on top
Only a few oils actually enter the hair fibre. Knowing which is which explains why coconut oil works as a pre-wash treatment and why argan oil does not.
The short answer
Coconut oil is the notable penetrator — its main fatty acid, lauric acid, is small and straight enough to pass into the cortex, where it reduces the protein loss that happens when hair swells with water. Most other oils, including argan, jojoba and olive, largely stay on the surface, which makes them sealants rather than treatments. Use penetrating oils before washing and sealing oils after.
Hair oiling is one of the oldest hair practices there is, and one of the least examined in the modern advice cycle, where every oil is described as though it does the same thing.
They do not. The most useful division in this category is between oils that get into the fibre and oils that stay on it — and it is a real, measurable distinction rather than a marketing one.
Why penetration matters
When hair gets wet it swells. Water enters the cortex, the fibre expands radially by several per cent, and the cuticle scales lift. Repeated swelling and drying is one of the routine mechanical stresses of having hair, and during it, some protein is lost from the fibre.
An oil that has penetrated the cortex occupies space and reduces how much water the fibre takes on. Less swelling means less protein loss and less cuticle lifting per wash. That is the mechanism behind pre-wash oiling, and it is why the timing is not a folk detail — the oil has to be in place before the water is.
An oil that stays on the surface does something different and also useful: it slows water leaving, reduces friction between strands, and adds shine. That job belongs after the wash.
Coconut oil for hair: the one that penetrates
Coconut oil is dominated by lauric acid, a straight, relatively small saturated fatty acid with a high affinity for hair protein. Its shape lets it move between the keratin structures rather than sitting on top of them. In the studies most often cited on this — measuring protein loss in hair treated with different oils before washing — coconut oil reduced protein loss in undamaged, bleached and chemically treated hair, while mineral oil and sunflower oil did not.
That is a narrow finding and it is worth stating precisely: coconut oil reduces protein loss during washing. It does not repair damage, it does not grow hair, and it does not seal split ends.
Practically: apply to dry hair, mid-lengths and ends, at least half an hour before washing, longer if you like. Then shampoo as normal. Warmth helps.
The caveat is real. A minority of people find that regular coconut oil leaves their hair stiff, dry and straw-like. It correlates roughly with the hair that also dislikes protein treatments, which fits the mechanism — both are adding rigidity to a fibre that did not want more. If that is your hair, this is not a technique problem to push through.
Babassu oil behaves similarly and is a reasonable alternative, and palm kernel oil shares the lauric acid profile. Avocado and olive oil show some penetration in some testing, less consistently.
The sealants
Everything else, essentially, and there is nothing wrong with being a sealant.
Argan oil — a light, pleasant finishing oil high in oleic and linoleic acid. It sits on the surface, adds shine, and has been marketed as considerably more than that.
Jojoba — technically a wax ester rather than a triglyceride, and structurally close to human sebum, which is why it feels natural on the scalp. Surface behaviour.
Sunflower, grapeseed, sweet almond — light surface oils, good for finishing fine hair where anything heavier would be visible.
Mineral oil — inert, very effective at slowing water loss, and the target of a great deal of unearned suspicion. It does not penetrate hair at all, which makes it a pure sealant and a good one.
Castor oil — thick, sticky, high in ricinoleic acid, and the subject of the most enthusiastic and least supported claims in this category. There is no good evidence it grows hair. It is a heavy sealant, and mixed with a lighter oil it makes a decent ends treatment.
How to actually use oils
Pre-wash, for protection. Coconut oil on dry lengths, 30 minutes to overnight, then wash. Once a week is plenty. This is the highest-value oil use for most people, and the one most often skipped in favour of the visible one.
Post-wash, for sealing. A very small amount of any light oil on damp ends, after conditioner and leave-in. On fine hair, a drop; on coily hair, considerably more. This is where oils belong in the "moisture sandwich" — last, over the water and the humectants, to slow the exit.
On the scalp, conditionally. Oiling a dry, tight scalp helps some people a great deal. Oiling a scalp with active seborrhoeic dermatitis usually makes it worse, because the yeast involved metabolises lipids. Know which scalp you have before adopting the ritual — the scalp guide sorts that out.
Not as a heat protectant. Oils have low smoke points and no meaningful thermal protection at styling temperatures. Applying oil before a straightener is a way of frying hair more efficiently.
The amount problem
Nearly every complaint about oils — greasy, limp, weighed down, will not wash out — is a quantity problem rather than a product problem. Hair needs vastly less oil than a palmful. Start with two drops, warm them between your hands, apply to the last few centimetres, and add more only if the hair looks unchanged.
Common questions
Does coconut oil work for everyone?
No. It suits porous, protein-tolerant hair, and a minority of people find it makes their hair stiff and straw-like — usually those whose hair does not want more protein-adjacent rigidity. Test on a section before committing to a full head.
Should I oil my scalp?
If it suits your scalp, yes, but understand the mechanism: oil does not feed follicles. It softens skin and may reduce flaking. On a scalp prone to seborrhoeic dermatitis, adding oil can feed the yeast involved and make things worse.
Is mineral oil bad?
No, and it is one of the better sealants — inert, non-comedogenic in the forms used, and very effective at reducing water loss. It does not penetrate, so it is a finishing product.
Does coconut oil make hair grow?
There is no good evidence that it does. What it does, and what the research actually supports, is reduce the protein your hair loses when it swells with water — which means less damage, less breakage, and more of the length you grow surviving. That is worth doing; it is not growth.
How do you use coconut oil for hair?
As a pre-wash treatment: a small amount on dry mid-lengths and ends, at least thirty minutes before washing, then shampoo as usual. Warm it between your palms first. Once a week is plenty, and the amount is far less than most tutorials suggest.
How much coconut oil should I use for a hair mask?
Roughly a teaspoon for shoulder-length hair, up to a tablespoon for very long or dense hair. If it takes two washes to remove, you used too much — and the second wash undoes some of what the oil was there to protect.
Kera offers hair-care lifestyle suggestions, not medical advice. It does not diagnose or treat any condition.