Which Oil Is Best for Hair Growth and Thickness?

September 29, 2026 Ishant Sharma

If you are asking which oil is best for hair growth and thickness, the short answer is rosemary oil for growth, and nothing convincing for thickness. Rosemary has the only human trial worth the name. Nothing has been shown in people to increase the diameter of a hair strand. Oils that cut breakage, such as coconut oil, make hair look fuller because you keep the length you grow.

Key Observations

Rosemary oil is the only oil with a published human trial for pattern hair loss, and that trial had no placebo group.
Pumpkin seed oil is sold everywhere for thickness. The one human trial that measured strand thickness found no change at all.
Peppermint, lavender and grapeseed evidence comes from mice, not people.
Coconut oil does not grow hair. It reduces protein loss, so you lose less length to breakage.
Most people apply oil to their lengths, then judge it as a growth failure. Growth claims depend on scalp application.
If your hair loss is driven by low ferritin, thyroid problems, postpartum shedding or PCOS, no oil will fix it.

Which oil is best for hair growth, and which is best for thickness?

Rosemary oil is the best-supported choice for growth, because it is the only oil tested against a real hair loss medicine in a human trial. For thickness, nothing has proven itself convincingly. The honest answer is that oils help you keep hair rather than grow thicker strands.

That split matters, because growth and thickness are two different things. Almost every guide treats them as one.

Growth means more hairs, or hairs staying in their growing phase longer. It is measured as hair count per square centimetre.
Thickness means the diameter of each individual strand. It is measured in micrometres.
Fullness is what you actually see in the mirror. It depends on both of the above, plus how much length you lose to breakage.

Oils have some preliminary evidence for the first. They have no good human evidence for the second. They have solid evidence for helping with the third, which is why they are still worth using.

Hair oil comparison table: what each oil is actually proven to do

This table separates what has been tested in people from what has only been tested in mice or in a laboratory dish. Most guides skip that distinction, which is how a mouse study becomes a headline about your hairline.

Oil	Best available evidence	Tested on	What it is genuinely good for	Watch out for
Rosemary oil	6 month trial against 2% minoxidil, 100 people (Panahi 2015)	Humans	The strongest case of any oil for hair count in pattern hair loss. A 2025 manufacturer-funded trial also reports thickness gains, with the caveats below	Must be diluted. Can irritate sensitive or eczema-prone scalps
Pumpkin seed oil	24 week trial, 76 men, taken as a capsule (Cho 2014)	Humans, but swallowed not applied	Hair count in men with pattern hair loss	The same trial measured thickness and found no change. Oral evidence does not transfer to a topical oil
Coconut oil	Laboratory testing on hair fibres (Rele 2003)	Hair strands in a lab	Reducing protein loss, so less breakage and better length retention	No growth evidence at all. Hardest oil to wash out
Peppermint oil	4 week study (Oh 2014)	Mice only	Promising, but unproven in people	Strong tingle. Easy to over-apply and irritate the scalp
Lavender oil	4 week study (Lee 2016)	Mice only	Promising, but unproven in people	A common contact allergen
Grapeseed oil	Cell and mouse study (Takahashi 1998)	Mice and lab cells	Light texture, good for fine hair that hates heavy oils	No human growth evidence
Castor oil	No published human growth trial	Not tested for growth	Coating and shine. Popular for edges and brows	Very thick. Linked to matting when used undiluted overnight
Argan oil	No published human growth trial	Not tested for growth	Softness, shine and frizz control on the lengths	Sold as a growth oil with no evidence behind that claim
Olive oil	No published human growth trial	Not tested for growth	Cheap pre-wash conditioning treatment	Heavy. Scent lingers. No growth evidence
Thyme, rosemary, lavender and cedarwood blend	7 month trial, 86 people (Hay 1998)	Humans, but a different condition	Alopecia areata, an autoimmune patchy hair loss	These results do not transfer to pattern hair loss or to general thickness

Do hair growth oils really work, or is it just the scalp massage?

This is the most useful question nobody asks. In the main rosemary trial, both groups massaged their scalps daily for six months, and no group did nothing at all. So the study cannot separate the oil from the massage, the routine, or simply the passage of time (Panahi 2015).

Scalp massage is not a trivial detail. It is a plausible part of why oiling routines appear to work, and it costs nothing. If you take one practical thing from this guide, make it the two minutes of massage rather than the oil itself.

A scalp massager brush makes this easier to do consistently, which matters more than the technique.

Does rosemary oil help hair growth?

There is one human trial suggesting it might. In 2015, researchers gave 100 people with pattern hair loss either rosemary oil or 2% minoxidil for six months. Both groups saw a similar rise in hair count, and the rosemary group reported less scalp itching (Panahi et al, Skinmed, 2015).

That study is the basis for almost every "rosemary is as good as minoxidil" headline you have seen. Before you rely on it, three things are worth knowing.

There was no placebo group. Everyone got something and everyone massaged their scalp. So we cannot tell how much of the improvement came from the oil itself.
The comparison was 2% minoxidil. That is the weaker formulation (Panahi 2015). Most people in the UK buy the 5% version.
It measured hair count, not strand thickness. Thickness was never assessed in that trial.

A separate laboratory study found that rosemary leaf extract inhibited the enzyme that converts testosterone into DHT, the hormone involved in pattern hair loss. That work was done in mice and in test tubes, and it used leaf extract rather than essential oil. Treat it as a reason for interest rather than proof (Murata et al, Phytotherapy Research, 2013).

How do you use rosemary oil for hair growth?

Apply diluted rosemary oil to your scalp, not your lengths, and massage it in for two minutes. Leave it for at least an hour, or overnight if that suits you. Then wash it out. Twice a week is enough, and consistency over months matters far more than how long you leave it on.

The most common mistake is applying oil to the mid-lengths and ends, which is where oil makes hair feel nice. Growth happens at the follicle, so scalp application is what the research actually tested.

How long should you leave rosemary oil in your hair?

One to two hours is enough for scalp contact. Overnight is not better in any proven way, and it is where most of the practical problems start: stained pillowcases, matted hair and a wash day that takes twice as long.

If you do go overnight, plait your hair loosely first and use an old pillowcase or a cap. UK forum users consistently name matting and ruined bedding as the reason they gave up on oiling.

How many drops of rosemary oil should you use?

Almost everyone uses far too much. As a starting point, use one to two pipettes of a blended oil for a short bob, and two to three for long or dense hair. You are aiming to dampen the scalp, not saturate the hair.

If you are diluting neat rosemary essential oil yourself, a widely used ratio is about 10 drops of essential oil per 10ml of carrier oil. That works out near 5% concentration, which is the upper end of what is generally advised for leave-on scalp use. Never apply neat essential oil straight to your scalp.

Pre-blended oils remove this step. Our Rosemary Ayurvedic Oil is already diluted into a base of sweet almond, pumpkin seed, castor, macadamia and avocado oils, with fenugreek, saw palmetto, nettle and horsetail extracts alongside biotin.

Can rosemary oil cause hair loss?

Rosemary oil is not known to cause hair loss, but it can irritate the scalp. An irritated or inflamed scalp is not a good environment for hair. People with eczema or sensitive skin report flare ups, so patch test behind your ear and wait 24 hours before your first full application.

There is a second reason people blame the oil. Applying it means handling your hair, and handling hair dislodges strands that were already due to shed. That shedding was going to happen anyway. If you are seeing genuinely increased loss over several weeks, that is worth a conversation with your GP rather than a change of oil.

If you are pregnant, breastfeeding, or managing a hormone-sensitive condition, check with a healthcare professional before using concentrated essential oils.

Is coconut oil good for your hair?

Coconut oil is good for reducing breakage, which is a real benefit, but it does not grow hair. Laboratory work on hair fibres found that coconut oil reduced protein loss where mineral oil and sunflower oil did not (Rele and Mohile, Journal of Cosmetic Science, 2003). Lauric acid binds to hair protein and is small enough to penetrate the strand.

That matters more than it sounds. If you lose two centimetres a month to breakage and grow one, you are going backwards. Reducing that loss is how most people gain visible length. It is retention, not growth, and the distinction is worth holding on to.

The catch is removal. Coconut oil is the oil people most often give up on, because it is genuinely hard to wash out. See how to get hair oil out below for the method that works.

Read more in our guide to coconut oil for hair.

Is castor oil good for hair?

Castor oil has no published human trial showing it grows hair. It is very thick and coats the strand well, which is why it feels like it is doing something and why it is popular for edges, brows and lashes. Treat it as a conditioning and sealing oil rather than a growth treatment.

Two practical warnings. Castor oil is one of the hardest oils to remove. Used undiluted overnight, it has also been linked to severe matting, sometimes called acute hair felting. Dilute it into a lighter oil rather than applying it neat.

More detail on our castor oil ingredient page.

Is argan oil good for hair?

Argan oil is excellent for softness, shine and frizz control, and it has no evidence at all for hair growth. It is widely marketed as a growth oil, which is a marketing decision rather than a scientific one. Use it on your lengths, not as a scalp treatment you expect results from.

For curly and wavy hair, argan works well as a finishing oil on damp hair after styling. It will not replace a leave-in, and it will weigh down fine hair if you use more than a few drops.

Is olive oil good for hair?

Olive oil is a cheap and effective pre-wash conditioning treatment, with no growth evidence behind it. It softens hair and makes detangling easier, which reduces breakage during combing. That is the whole benefit, and it is a reasonable one.

It is heavy, the scent lingers, and it needs a proper wash to remove. If you like the results but not the smell, a blended formula with a lighter base will usually suit you better.

Which oils are tested on humans and which are only tested on mice?

Only rosemary oil, pumpkin seed oil and one four-oil blend have human trials. Peppermint, lavender and grapeseed evidence comes from mice. This distinction is missing from almost every article on this topic, and it is the main reason people expect results that were never demonstrated in a person.

Mouse hair grows in synchronised cycles. That makes mice convenient to study and a poor stand-in for a human scalp. A mouse result is a reason to run a human trial. It is not a reason to promise anything.

Evidence level	Oils	What you can reasonably expect
Human trial, relevant condition	Rosemary oil	Possible improvement in hair count over about six months
Human trial, but oral, and thickness was null	Pumpkin seed oil	Do not expect a topical oil to reproduce a capsule result
Human trial, different condition	Thyme, rosemary, lavender, cedarwood blend	Evidence applies to alopecia areata only
Laboratory, hair fibres	Coconut oil	Less breakage, better length retention
Mice and cells only	Peppermint, lavender, grapeseed	Unproven in people
No growth evidence	Castor, argan, olive	Conditioning benefits only

Can any oil actually make your hair strands thicker?

No oil has convincingly been shown to increase the diameter of your hair strands. One trial does claim it, and it is worth looking at properly before you rely on it. The clearest independent test came from the pumpkin seed oil trial. It measured strand thickness directly over 24 weeks and found no difference at all between the treatment group and the placebo group.

Both groups came out at 0.34, with a p value of 0.991. That is about as flat a result as research produces. The same trial did find a 40% rise in hair count against 10% for placebo, so it was not a failed study. It simply found growth without thickness (Cho et al, Evidence-Based Complementary and Alternative Medicine, 2014).

Two caveats are worth stating. The trial was funded by the company supplying the capsules. It also tested an oral supplement, not an oil applied to the scalp.

The exception worth naming is a 2025 trial on a branded rosemary and lavender blend, which reported a 68.70 percent gain in hair thickness over 90 days (Patel et al, Cureus, 2025). Three things temper it. The company that sells the product funded the study and employs two of the four authors. The coconut oil placebo group also improved significantly on every measure, including a 24.34 percent thickness gain. And the reported p values compare each person against their own baseline rather than comparing the groups against each other, with no between-group test published.

So it is not nothing, and it is not proof. If a placebo produces a 24 percent thickness gain in the same trial, the measurement is doing a lot of the work.

So when a product promises thicker hair from an oil, what it can honestly deliver is hair that looks thicker. More strands surviving, less breakage, better length retention and a healthier scalp. That is a genuine result. It is not the same as a thicker strand, and we would rather say so.

How we checked this guide

We read the primary studies behind every claim on this page rather than relying on other people's summaries of them. That is how we found that the pumpkin seed oil trial, which is quoted everywhere as proof of thicker hair, measured thickness and reported no change.

We also checked the year and preparation on the rosemary and DHT research, because several widely shared articles cite it as a 2012 essential oil study. It was published in 2013 and it tested leaf extract. Where a study was done in mice or in a laboratory dish, we have said so in the same sentence as the finding rather than in a footnote.

What do UK users actually report?

Published trials tell you what happens under supervision. UK discussion threads tell you why people stop. The pattern in those threads is consistent, and it is rarely about whether the oil works.

Removal is the number one complaint. One Mumsnet poster described coconut oil as "MURDER trying to wash it out afterwards".
Dose is usually far too high. Experienced users talk about a few drops or one pump, not a palmful.
Roots are the wrong target for shine. One poster advises to "Avoid using on the roots" because it looks greasy.
Results take longer than people expect. On a thinning hair thread, one reply put it plainly: "If something is working, you won't know for about a year".
Some people react badly. Reports on one rosemary oil thread include an eczema flare and a scepticism that it does anything for growth at all.
Oil in shampoo is treated as pointless. As one poster puts it, it will not work in shampoo because that is a wash on, wash off product.

None of this means oils are useless. It means the failure is usually in the method, the dose or the timescale, not the bottle.

How do you get hair oil out without stripping your hair?

Put shampoo onto dry, oiled hair first, work it through, and only then add water. Adding water first makes the shampoo slide over the oil instead of binding to it. That is why people end up washing three times and still feel greasy.

This is the single most common reason people abandon oiling, and it is almost never covered. The method, sometimes called reverse washing, takes one attempt to learn.

Stand in the shower with dry hair and the water off.
Apply shampoo directly to the oiled areas and massage it in properly.
Add a little water and keep working it until it turns milky.
Rinse thoroughly, then do a second, much smaller shampoo if you need one.
Condition the lengths as usual.

If you use a shampoo bar, rub the bar straight onto the dry oiled sections rather than building lather in your hands first.

How long does it take to see results from hair oil?

Give it three months minimum, and judge it properly at six. Hair grows roughly one centimetre a month, so anything shorter than three months is too short to show a change that is not just normal variation.

The human trials here ran for six and seven months. That is the timescale to plan around. It is also why a photo on day one, under the same light and in the same spot, beats any product claim.

Timeframe	What is realistic
Weeks 1 to 4	Softer hair, less frizz, a calmer scalp. No growth change yet.
Weeks 4 to 12	Less breakage when detangling. Ends holding up better.
Months 3 to 6	The earliest point at which a change in density might show.
Month 6 onwards	If there is no change at all by now, the oil is not your answer.

When is hair oil not the answer?

If your hair loss has a medical driver, an oil will not fix it. Low ferritin, thyroid conditions, postpartum shedding, PCOS, menopause, crash dieting and certain medications all cause hair loss that no topical product addresses. Treating the cause is what works.

Signs it is worth seeing your GP rather than buying another bottle:

Sudden or patchy loss, rather than gradual thinning
Noticeable shedding two to four months after illness, childbirth, surgery or major stress
A widening parting alongside fatigue, heavy periods or unexplained weight change
Scalp pain, scaling, redness or visible scarring
Loss of eyebrow or body hair as well

Iron, ferritin and thyroid function are all blood tests your GP can run. That is a better first step than a sixth oil.

How do you oil your hair without greasy roots or ruined pillowcases?

Use less than you think, apply to the scalp in sections rather than pouring it over your head, and wash it out rather than leaving it in. Greasy roots are almost always a dosage problem, not an oil problem.

What works in practice:

Part your hair in sections and apply straight to the scalp with a nozzle or pipette.
Massage for two minutes so the oil spreads thinly instead of sitting in patches.
If you want shine on your lengths, that is a separate few drops, on damp mid-lengths and ends only.
Plait loosely before bed if you are leaving it overnight.
Use an old pillowcase or a satin cap. Oil stains do not fully come out of cotton.
Fine hair usually does better with a one hour treatment before washing than an overnight one.

Where can you buy rosemary oil in the UK?

Rosemary oil is widely available in UK pharmacies, health shops and online. The thing to check is whether you are buying neat essential oil, which must be diluted before use, or a pre-blended scalp oil that is ready to apply.

Neat rosemary essential oil is cheaper per millilitre but needs mixing with a carrier oil. Getting that ratio wrong is the most common cause of scalp irritation. A blended formula removes the risk and usually includes supporting ingredients.

Our Rosemary Ayurvedic Oil is a 100ml blend at £23.00. It is formulated with sweet almond, pumpkin seed, castor, macadamia and avocado oils, plus fenugreek, saw palmetto, ashwagandha, nettle and horsetail extracts and biotin. It is free from sulfates, parabens and mineral oil, and it suits hair and beards.

If your main concern is comfort on a dry scalp rather than growth, look for a lighter base such as grapeseed or black seed oil rather than a heavy castor or coconut blend. Pair whichever oil you choose with a scalp massager brush, since the massage is the part of the routine with the least doubt attached to it.

UK orders over £35 ship free, and every order is covered by our 75 day money back guarantee. That is long enough to actually test whether an oil works for you.

Frequently asked questions about oils for hair growth and thickness

What does rosemary oil do for your hair?

Applied to the scalp, rosemary oil has one human trial behind it showing an increase in hair count over six months. It does not change the thickness of individual strands, and it does not condition the lengths the way a carrier oil does.

Does rosemary oil actually work, or is it a trend?

There is one genuine human trial behind it, which is more than most oils have. That trial had no placebo group, so the result is promising rather than settled. It is reasonable to try, and unreasonable to expect a transformation.

Can I just add rosemary oil to my shampoo?

No. Shampoo is rinsed out within a minute or two, so the oil has almost no contact time with your scalp. Apply it as a leave-on or pre-wash treatment instead.

How often should I oil my hair?

Twice a week is enough for most people. Daily oiling does not speed anything up, and it makes buildup and greasiness far more likely.

Should I put hair oil on wet or dry hair?

Apply scalp treatments to dry hair, since water on the scalp dilutes the oil and makes it harder to place accurately. For shine on the lengths, damp hair works better.

Does hair oil cause hair loss or shedding?

Oil does not cause shedding, but applying it means handling your hair, which dislodges strands that were already ready to fall. If shedding keeps increasing over several weeks, speak to your GP.

Is coconut oil or rosemary oil better?

They do different jobs. Rosemary oil is the growth candidate and goes on the scalp. Coconut oil reduces breakage and goes on the lengths. Many people use both, for different reasons.

Can hair oil help a dry, itchy or flaky scalp?

A lighter oil can help with dryness and comfort. Persistent flaking, itching or soreness should be checked by a pharmacist or GP rather than treated with oil indefinitely.

How long should I leave rosemary oil in my hair?

One to two hours is plenty. Overnight is optional and brings matting and pillowcase problems without any proven extra benefit.

Will hair oil help if my hair loss is hormonal?

Probably not on its own. Hormonal hair loss, including PCOS and menopause related thinning, needs the underlying cause addressed. An oil may support scalp health alongside that, but it is not a treatment.

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