What Is Castor Oil, What Does It Do? The Eyelash Growth Claim

What distinguishes castor oil, labelled Ricinus Communis (Castor) Seed Oil on the label, from other vegetable oils is the dominance of a single fatty acid: about 90% of its fatty acids are ricinoleic acid. This acid carries a hydroxyl group in its chain, which makes the oil unusually thick. That is why it is preferred in products such as lipsticks. Although the seed contains the toxic protein ricin, in oil extracted by the commercial method ricin is either very low or absent. Still, this is a cosmetic oil and must not be ingested: fatal cases linked to castor oil tea given to newborns have been published.

Does castor oil lengthen eyelashes and eyebrows?

This is the most frequently asked question, and the answer is: we know of no controlled human study showing it. A current review of the dermatological use of castor oil includes no data on eyelash or eyebrow growth at all. The path the claim follows is this:

1. Starting point: Higher prostaglandin D2 was shown on balding scalp.
2. Link: Computer modelling and laboratory data suggested that ricinoleic acid may bind the enzyme that makes this substance.
3. Broken link: A controlled study in male-pattern hair loss with a drug targeting the same pathway showed no effect. There is no comparative study done on eyelashes or hair with castor oil.

There is also a finding confused with eyelash growth: in 26 people with blepharitis (inflammation of the eyelid margin), castor oil applied around the eye for 4 weeks reduced eyelash sticking and eyelash loss. This result concerns eyelids with disease; it does not show that it lengthens healthy eyelashes. Prescription eyelash products work through a different mechanism; details are on the eyelash serum page. The oil making lashes look glossy and full is an appearance effect. Home-use oil is not sterile, so do not let it get into the eye. If there is redness or crusting on the eyelid, consult your doctor first.

What does it really do to hair?

The only clearly measured effect is shine: in a study measuring light reflection, castor oil increased contrast on hair strands. Most uses for moisturising, itching and dry scalp have not been clinically tested. We know of no human study on hair growth or stopping shedding. If hair is shedding markedly, read the reason in the hair loss article and see a dermatologist.

The thickness also has a price. A case was published in which hair became completely matted after castor oil and coconut oil were applied, and the hair had to be cut. It is very rare, but it is reason enough not to apply a thick layer to long, tangle-prone hair. Apply a small amount, only to the ends.

Who may react to castor oil?

• Users of lip products: In one person who had itching, darkening and swelling of the lip for more than a year, ricinoleic acid and several lipsticks tested positive in a patch test. If you have recurring lip problems with lipstick, bring the ingredient list to your dermatologist.
• People who have reacted before: There are contact dermatitis cases linked to deodorants, ear drops and dressings. In general it is rare and mild. The US cosmetic safety panel finds the oil safe at the concentrations used, and sensitisation in humans and animals is low.
• Beginners: Before applying it to your face or around the eyes, try it on the inner arm, twice a day, for 7-10 days.

Hydrogenated Castor Oil, PEG-40 Hydrogenated Castor Oil or Zinc Ricinoleate that you see on labels are not the same oil. These are derivatives used as thickeners, solvents or fragrance fixatives, and none of the claims above is based on them.