You've probably seen the videos: someone applies a thick layer of castor oil to their hairline, wraps a shower cap around it, and leaves it overnight. A few weeks later, the comparison follows: thin on the left, full on the right. Castor oil, also known as miracle oil, is now mentioned as often as rosemary oil when you're looking for something against hair loss without medication.
The problem is that "miracle oil" is a marketing name, not a scientific term. We investigated what is truly known about castor oil and hair growth, and what a 2025 study recently added to that knowledge.
What exactly is castor oil?
Castor oil is pressed from the seeds of the castor bean plant (Ricinus communis) and consists mostly of ricinoleic acid, a fatty acid that does not occur in such high concentration anywhere else. This substance is known for its anti-inflammatory and moisturizing properties. It is a thick, sticky oil that has traditionally been used as a laxative and a remedy for dry skin, long before anyone thought of applying it to a scalp.
Why would it help against hair loss?
The idea behind castor oil for hair loss is that ricinoleic acid improves blood circulation in the scalp, providing hair follicles with better oxygen and nutrient supply. Additionally, the oil is supposed to soothe an inflamed or irritated scalp, which in itself is beneficial for hair growth. Both mechanisms are plausible, but plausible is not the same as proven.
What does research into castor oil alone say?
Here's the honest answer: there is no published research showing that castor oil by itself makes hair grow faster, prevents hair loss, or makes hair thicker. What there is are older studies on ricinoleic acid that show it can give hair a temporary, superficial shine by forming a layer around the hair shaft. This is a cosmetic effect, not a biological effect on the hair follicle.
Much of what you read online about castor oil and hair growth is therefore based primarily on experiences, not on clinical research. That's not to say those experiences are made up, but a fuller-looking hairstyle after a night with oil in it says little about what's happening in the hair follicle itself.
The new study: castor oil in combination with rosemary
In 2025, a double-blind, placebo-controlled study with ninety participants, divided into three groups of thirty, was published in the journal Cureus. One group used an oil with rosemary and castor oil for ninety days, a second group rosemary with lavender, and the third group coconut oil as a comparison. The hair growth rate in the rosemary-castor oil group increased from 0.23 to 0.33 millimeters per day, an increase of almost 48 percent. Hair thickness increased by 66 percent and hair density by over 32 percent, measured with a phototrichogram by an independent dermatologist.
Those are solid numbers. But if you read the study carefully, it becomes clear that it was not about castor oil alone. It was about a mixture of rosemary and castor oil, compared to coconut oil, not with a neutral placebo or nothing at all. Rosemary oil itself has already built a separate reputation in other research, so it's hard to say what part of this result comes from the castor oil and what part from the rosemary. The study was also conducted around a commercial product called Rosmagain, which doesn't automatically mean the results are unreliable, but it is a reason not to blindly accept them.
What you can take away from this
Castor oil alone has no proven effect on hair growth. Castor oil in combination with rosemary oil did show clear improvement in growth rate, thickness, and density in one recent study, although an independent follow-up study confirming this is lacking. For now, the fairest summary is: castor oil is probably not harmful to try, but don't expect too much from it on its own. Most evidence points to rosemary as the more active component.
How to use castor oil safely if you still want to try it
Castor oil is thick and sticky, so a small amount is enough. Here's how to do it:
- Mix a teaspoon of castor oil with a lighter carrier oil, such as jojoba oil, to make it more spreadable.
- Massage it gently into the scalp, not into the hair lengths.
- Leave it on for at least a few hours, or overnight if your skin tolerates it well.
- Then wash it out thoroughly with shampoo. One wash is often not enough to completely remove the oil.
First, do a patch test in your elbow crease if you've never used castor oil before. Some people get folliculitis, small inflamed bumps around the hair follicle, because the thick oil can clog pores. If you notice this, stop immediately.
Do not apply castor oil just before or after minoxidil or a serum. The thick layer can hinder the absorption of other active substances into the scalp.
Does this fit alongside a serum or derma roller?
If you want to try castor oil alongside your existing routine, you can, as long as you consider the timing mentioned above. Do not use it on the same day just before or after rolling with a derma roller, because a damaged scalp and a thick layer of oil don't go well together.
For most men with early hair loss, a targeted formula is more practical than finding individual oils. Our Growth Serum contains rosemary oil, among other ingredients, along with nine other active substances that act on the hair growth cycle in different ways. That's not a promise that it works faster than a homemade oil mixture, but it is a way to not depend on a single oil whose evidence is still thin.
Conclusion
Castor oil by itself has no proven effect on hair growth, despite what you see on TikTok. There is a recent study in which castor oil combined with rosemary oil showed clear improvement, but these results have not yet been independently confirmed and say little about castor oil as a standalone remedy. If you still want to try it, do so diluted, with a patch test beforehand, and with realistic expectations. For structural improvement in hereditary hair loss, a well-supported formula or medication is still the better-researched route.
Frequently Asked Questions
Can castor oil clog your pores?
Yes, it can. Castor oil is thick and, if used excessively, can clog the pores around the hair follicle, which can cause folliculitis, small red or inflamed bumps on the scalp. Use it in moderation, wash it out thoroughly, and stop if irritation occurs.
Does Jamaican black castor oil work better than regular castor oil?
There is no research that has specifically compared this. Jamaican black castor oil is roasted before pressing, which changes its smell and color and, according to users, gives it a stronger effect, but a scientific comparison between the two variants on hair growth is lacking.
Can you use castor oil on your eyebrows or beard for the same effect?
Yes, you can apply it in the same way, but the evidence for a growth effect is as thin there as for scalp hair. It can, however, provide a well-groomed, shiny appearance without actual new growth. Again, use a small amount; the skin around the eyes and jaw is more sensitive than your scalp.
How do you wash castor oil out of your hair thoroughly without it feeling greasy?
First apply shampoo to the dry oil before adding water; this helps the oil bind better. Then shampoo twice and rinse thoroughly. One wash is often not enough to remove all the oil.
Is castor oil safe to use during pregnancy for the scalp?
Topical use on the scalp is generally considered safe, unlike ingesting castor oil, which can induce labor and is therefore not recommended during pregnancy. The risk is primarily in drinking the oil, not in applying it to your skin or scalp. If in doubt, always consult your midwife or general practitioner, especially if you are using multiple products at the same time.
Can you mix castor oil with minoxidil?
No, do not mix them directly. Apply them at different times of the day, as the thick oil layer of castor oil can interfere with the absorption of minoxidil into the scalp and thus reduce its effectiveness. For example, use minoxidil in the morning and castor oil only in the evening, ensuring enough time between the two products.
Why does my hair feel thicker after castor oil even if there is no new growth?
This is due to the layer that ricinoleic acid forms around the hair shaft, making existing hair feel thicker and fuller. This is a cosmetic effect on the hair shaft itself, not a sign that new hair follicles have become active. Once you stop using it, that full feeling usually disappears quite quickly.
How often per week is it best to use castor oil?
Once to twice a week is enough for most people. Using it more often does not make it more effective and mainly increases the chance of clogged pores or an irritated scalp, especially if you don't wash out the oil properly. Start with once a week and only increase if your scalp tolerates it well.
Is there a difference between cold-pressed and refined castor oil for your scalp?
Cold-pressed castor oil retains more of the original nutrients and has undergone fewer processing steps, which users often find gentler on the skin. Refined castor oil is cheaper and has a longer shelf life but lacks those extra nutrients. There is no direct scientific comparison between the two variants on hair growth, so the choice is mainly a matter of preference and skin sensitivity.
Can you combine castor oil with a derma roller?
Not on the same day. Never roll just before or after applying castor oil, as the small wounds from rolling, combined with a thick oil layer, can cause irritation or an increased risk of infection. Allow at least a day between them.
