Does castor oil cause hair yellowing?

The castor oil (INCI: Ricinus Communis (Castor) Seed Oil) is a plant oil obtained by cold pressing the seeds of the castor plant (Ricinus communis), a shrub cultivated in China, India, and Brazil. From an organoleptic perspective, castor oil appears as a thick yellow liquid and is noted for its nourishing and strengthening properties, which derive from its saturated fatty acids. These fatty acids share a chemical structure with cuticle lipids, allowing insertion by biomimicry to reinforce this layer’s cohesion. Moreover, although additional studies are needed, the castor oil could stimulate hair growth, a property that contributes to its popularity. This effect is due to its ability to inhibit prostaglandin D2 (PGD2), a protein involved in androgenetic alopecia.

Despite its many benefits for hair, castor oil faces criticism for its thick, viscous texture and its alleged yellowing effect. Nevertheless, this effect has never been reported or demonstrated in scientific studies.

Only a few reports mention the yellowing effect of castor oil when applied in large quantities and left on hair for long periods. It is hypothesized that this depends on natural hair pigmentation, light or bleached hair being more likely to pick up tint, their porosity, as porous hair absorbs more product on its surface, and on hair fiber oxidation, oxidized hair being more fragile. The apparent yellowing noted by some could also be an optical effect. Indeed, the castor oil has a natural yellow hue when applied to the hair, it may create a temporary yellowing effect, especially if the rinse is incomplete. However, without scientific studies on the subject, these are only hypotheses.

Although no scientific evidence supports that castor oil can cause hair yellowing, here are some tips to keep benefiting from its effects when applied to hair.

• Apply only a few drops of castor oil.

  Castor oil has a high lipid content and an oily texture, so a small amount suffices. Excess can weigh hair down or may yellow strands. Applied at the roots to stimulate growth or along the lengths to nourish, it requires a few drops.

• Wash hair after applying castor oil to remove residue.

  According to some reports, leaving it on too long or an inadequate follow-up shampoo may promote hair yellowing. To prevent this, focus on areas where you applied castor oil during shampooing and rinse with plenty of water. Some people use two consecutive shampoos to remove all castor oil residue.

• Avoid pure castor oil on color-treated hair.

  As a precaution, people with color-treated hair may substitute castor oil with another plant oil for hair care, such as hibiscus oil or mustard oil. Another option is diluting castor oil in a plant oil at a 20% concentration. This lets you safely benefit from castor oil’s haircare properties.

• Check the quality of the castor oil used.

  Finally, to reduce the risk of hair yellowing, we recommend using castor oil that is high-quality, cold-pressed, and filtered to prevent impurities from adhering to hair fibers.

• JOEKES I. & al. Yellowing and bleaching of grey hair caused by photo and thermal degradation. Journal of Photochemistry and Photobiology B: Biology (2014).

• MARWAT S. K. & al. Review - Ricinus communis - ethnomedicinal uses and pharmacological activities. Pakistan Journal of Pharmaceutical Sciences (2017).

• TESSEMA S. S. & al. Physicochemical characterization and evaluation of castor oil (R. communis) for hair biocosmetics. American Journal of Applied Chemistry (2019).