Bio Oil: More Snake Oil than Duck Oil

Posted by Dr Steve Humphries on 7th Mar 2022

Bio Oil is a popular skincare oil that is promoted as helping to improve the appearance of scars, stretch marks and uneven skin tone. But just how good is it? By looking at the ingredients we can see it is certainly not a quality natural product. The main ingredient is mineral oil (aka liquid paraffin – a petroleum distillate).

So a mineral oil product is called ‘Bio Oil’ – I think that’s called irony. Why put mineral oil on your skin when there are so many wonderful moisturizing plant oils; like jojoba oil, or coconut oil. Perhaps the commercial answer is that mineral oil is formulated into cosmetic products because it is as cheap as chips (though you may well have paid a lot for it).

Bio Oil is claimed to contain the unique and breakthrough ingredient PurCellin Oil™. But ‘PurCellin’ is just a made-up trade name used for marketing, and the people that sell Bio Oil are rather coy about identifying which ingredient in their product it is. But a check of the patent literature shows that purcellin oil is listed as cetearyl octanoate (now known by its more recent name cetearyl ethylhexanoate) – and a listed ingredient in Bio Oil.

Far from being a unique and breakthrough product this is a very common synthetic emollient used in the formulation of a wide range of skin and hair care products. It is sold commercially in bulk to personal care product manufacturers under a number a trade names, including Crodamol™ CAP, Tegosoft® Liquid and Luvitol® EHO.

And indeed the Bio Oil website makes no specific claim for PurCellin Oil™ other than it “changes the formulation’s overall consistency, making it light and non-greasy” (retrieved 12 Aug 2014). This is why cosmetic formulators use cetearyl ethylhexanoate in their synthetic products, but this is hardly the ‘breakthrough ingredient’ for people wanting to improve the appearance of scars, stretch marks and uneven skin tone.

Here come the ducks

duck oilBio Oil has been widely touted as being derived from, or based on, duck preening oil. If we had feathers maybe this would make more sense but anyway to understand the duck connection we need to cover a bit of chemistry. Esters are a very common class of compound in nature – all oils and waxes are esters. An ester is a combination of an alcohol and an acid. Cetearyl ethylhexanoate (PurCellin Oil) is a synthetic ester, it is a combination of cetyl and stearyl alcohols with 2-ethylhexanoic acid.

Duck preening oils are a complex mixture of many compounds that include a range of natural wax esters, though not cetearyl ethylhexanoate. So here is the tenuous connection: synthetic cetearyl ethylhexanoate (PurCellin Oil) is an ester and it repels water, duck preening oil contains other different esters and it also repels water! In fact all (ester) waxes repel water. It has to be said that the silly duck story is not on the current Bio Oil website - it was always more marketing hype than good chemistry or good sense.

In sum Bio Oil does not contain any unique or breakthrough ingredients, in fact it is a fairly standard mix of commercially available synthetic ingredients in a mineral oil base with a few natural ingredients tossed in for good measure. On this basis we wouldn’t expect it to perform any better than many other similar, and less costly, products on the market.

Here comes the research

One of the main claims of Bio Oil is that it can improve the appearance of stretch marks so I retrieved their latest stretch mark research form their Bio Oil website (Visit website Retrieved 12 Aug 2014 )

Let’s have a read of their study and evaluate the claims.

Trial centre
proDERM institute for applied dermatological research, Hamburg, Germany.

To assess the efficacy of Bio Oil in improving the appearance of stretch marks.

Subjects: 38 female participants of varying ethnicities. Age of participants: 18 to 65. Stretch mark causes: various (post pregnancy, weight gain or adolescent growth spurt). Stretch mark locations: abdomen, thigh and hips.

Double-blind, randomized and placebo controlled. Subjects had matching stretch marks or a stretch mark large enough to allow a half-half stretch mark application and intra-subject comparison. Product was applied twice daily for 8 weeks, no additional massaging performed on the target area. Application performed under supervision at regular intervals. Assessments conducted at 0, 2, 4 and 8 weeks. Different scar parameters as defined in the Patient and Observer Scar Assessment Scale (POSAS) were evaluated.

Bio Oil is efficacious in improving the appearance of stretch marks. A statistically significant result after only 2 weeks (day 15), evident in 95% of the subjects. After 8 weeks (day 57) 100% of subjects showed an improvement, with the extent of the improvement more than double that at 2 weeks. A continuous improvement of POSAS over the duration of the study.

Well using a double-blind, randomized and placebo controlled trial, the gold standard of scientific methodology, certainly sounds good. They are talking the talk, but are they walking the walk?

In fact there are a number of problems with the study and the results:

While it is said that there were significant improvements no actual magnitude of change was given. The POSAS scale they used measures the amount of change and yet we are not provided with that crucial information. I assume whatever change there was wasn’t worth reporting.

2) It claims to be a placebo controlled study and yet the placebo condition is not defined! It is important to know what the Bio Oil treatment is being compared to. Is it being compared to another competing product, or perhaps a mineral oil base without PurCellin (that would be interesting).

3) The results do not compare the Bio Oil to the placebo control!!! And that is the whole point of a double-blind, randomized and placebo controlled study. All we are given is that there is some appearance improvement over time using the Bio Oil. But rubbing any oil or lotion into the skin is likely to have that effect. Given the placebo comparison is not reported I’m assuming the Bio Oil did no better than the comparison treatment – surely they would tell us if it did.

On the basis of the presented results it is clear the testing company is working in the interests of the people that sell Bio Oil, not the consumers. “He who pays the piper ....”

There are a number of other faults with Bio Oil but these have been adequately covered on other websites. Suffice to say that if you are looking for a quality natural product then you won’t be interested in Bio Oil.

Dr Steve Humphries

Hebe Botanicals Ltd