Encyclopedia · oil or butter
Coconut oil
The best-studied hair oil; in lab work it cut protein loss and fatigue damage when used before washing, but almost all studies come from coconut-oil sellers.
What it is
A triglyceride oil dominated by lauric acid, a 12-carbon saturated fatty acid. It is sold as virgin (unrefined), refined or fractionated (liquid at room temperature) oil. It is a cosmetic ingredient with no restrictions for hair use in the US, EU or UK.
How it works
Lauric acid is small and straight-chained, so it diffuses into the cement between hair cells and binds protein better than hydrocarbons, according to the original authors. Rele 2003 Ion imaging showed coconut oil reaching the inside of fibres where mineral oil did not. Ruetsch 2001 It also limited swelling, which may reduce swelling-related fatigue.
What the studies show
- Only coconut oil, of three oils tested, reduced protein loss in damaged and undamaged hair as a pre- or post-wash treatment; mineral and sunflower oil did not. Industry study (Marico). Rele 2003
- Coconut oil penetrated hair cross-sections; mineral oil did not. Ruetsch 2001
- Coconut, olive and sunflower oil films thinned over time (consistent with absorption), while mineral oil did not. Keis 2005
- After 20 washes, coconut oil raised the tensile strength of twisted fibres versus mineral oil or washing alone (Marico). Kaushik 2021
- A coconut-based oil prevented the wash-induced porosity increase, reversed loss of break stress and protected colour (Marico). Kaushik 2022
- Coconut oil triglycerides penetrated the cement between cells and improved fatigue strength (Procter & Gamble), but other plant oils did too. Marsh 2024
- A 2022 systematic review of 22 articles found limited clinical evidence that coconut oil treats brittle hair. Phong 2022
See oils and hair. No randomised head-to-head human trial of hair oils exists.
How it's used in studies
Studies used pre-wash application to dry hair, with amounts set per tress weight. Common practice is 30 minutes to overnight before washing, or 1-3 drops on the ends after washing. There is no standard dose, and the studies were done on cut hair.
Side effects and safety
Generally well tolerated, and contact allergy is uncommon. It is comedogenic on facial skin for some people (not hair-specific). It can feel stiff or greasy on fine or low-porosity hair (anecdotal). Do not apply to a scalp prone to seborrhoeic dermatitis without advice. It is not a heat protectant.
Bottom line
It is the best-supported oil for pre-wash use on damaged, colour-treated, coarse or high-porosity hair, and it is cheap. Treat it as a cosmetic aid for breakage and frizz, not a repair. We are only moderately sure, because the lab studies come mostly from the industry that sells it. Whether coconut oil is special or any penetrating triglyceride works is unsettled.
Studies 7
Rele AS, Mohile RB. Effect of mineral oil, sunflower oil, and coconut oil on prevention of hair damage. J Cosmet Sci. 2003
Tested: mineral, sunflower and coconut oil
Result: Mineral oil did not reduce protein loss from combing in either undamaged or damaged hair; coconut oil did.
Read the study ↗Ruetsch SB et al. SIMS investigation of penetration of coconut and mineral oils into human hair fibers. J Cosmet Sci. 2001
Tested: coconut oil vs mineral oil
Result: Coconut oil penetrated the hair fibre; mineral oil did not.
Read the study ↗Keis K et al. Investigation of penetration abilities of various oils into human hair fibers. J Cosmet Sci. 2005
Tested: several oils
Result: Oil films thicker than about 0.5 micrometres hid the cuticle scale structure, and the film thinned as oil soaked in, faster with heat.
Read the study ↗Kaushik V et al. Single hair fiber assessment techniques to discriminate between mineral oil and coconut oil. J Cosmet Dermatol. 2021
Tested: coconut oil vs mineral oil across washes
Result: Coconut oil, not mineral oil, strengthened twisted fibres across washes.
Read the study ↗Kaushik V et al. Benefit of coconut-based hair oil via hair porosity quantification. Int J Cosmet Sci. 2022
Result: Repeated surfactant washing raised pore surface area in an industry study; pre-treatment with coconut-based oil limited it.
Read the study ↗Marsh JM et al. Penetration of oils into hair. Int J Cosmet Sci. 2024
Tested: pure plant triglyceride oils including coconut, Camellia oleifera and safflower
Result: Several plant oils entered the hair's lipid-rich cement and improved single-fibre fatigue strength; shorter and unsaturated chains penetrated better.
Read the study ↗Show 1 more studies
Phong C et al. Coconut, castor, and argan oil for hair in skin of color patients: a systematic review. J Drugs Dermatol. 2022
Tested: coconut, castor and argan oil for hair
Result: Weaker evidence that castor oil improves luster and no strong evidence for growth.
Read the study ↗Related
- Mineral oilA cheap, non-penetrating hydrocarbon oil that coats hair for shine and slip but, unlike coconut oil, did not protect against protein loss in lab tests.
- Sunflower seed oilIn the classic Marico study sunflower oil did nothing for protein loss, though later work suggests oils of its type can penetrate hair.
- Olive oilA traditional hair oil whose only supporting hair data is that its film thinned on hair like coconut oil did, suggesting some absorption.
- Oils and hairOils coat hair and some enter it, which can cut damage from washing, but they do not repair split ends or add moisture.
- Leave-ins, masks and layering methodsMasks and leave-ins use the same conditioning chemistry as rinse-off conditioner; layering methods like LOC rest on consumer satisfaction, not trials.