What it is

An oleic-acid-rich oil from olives, long used for hair in Mediterranean and Middle Eastern traditions. It is a cosmetic ingredient.

How it works

A capillary-adhesion study found that olive oil films between fibres decreased with time, as for coconut and sunflower oil but not mineral oil, consistent with absorption into the fibre. Keis 2005 Pure triolein, the main olive triglyceride, penetrated the cement between hair cells in a Procter & Gamble study. Marsh 2024

What the studies show

Olive oil adhesion between fibres decreased over time like coconut and sunflower oil, and unlike mineral oil. Keis 2005
Labelled triolein penetrated the cement between cells. Marsh 2024
We found no olive-oil-specific hair efficacy study. Claims rest on indirect work (see oils and hair).

How it's used in studies

Traditional use is warmed oil on dry hair before washing. There are no controlled consumer-dose data.

Side effects and safety

Low risk. It is heavy, hard to wash out and builds up on fine hair.

Bottom line

A reasonable cheap pre-wash or end-sealing oil for thick, coarse or curly hair. We are not very sure it does more than other oils.

Studies 2

Keis K et al. Investigation of penetration abilities of various oils into human hair fibers. J Cosmet Sci. 2005

Design: in vitro
Who: human hair fibres, laboratory

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 ↗

Marsh JM et al. Penetration of oils into hair. Int J Cosmet Sci. 2024

Design: in vitro
Who: human hair, Procter & Gamble laboratory

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.