The evidence
Every number, and where it came from.
This page exists because most skincare efficacy numbers are printed in a large font with no paper attached. Everything below is the paper. Where the evidence stops, this page says where it stops.
37.8%
less water lost through the skin surface, 24 hours after one application
Shea butter at 20 mg/cm², on a Tewameter TM 300. Water loss fell from 8.2 to 5.1 g/m²/h, p < 0.01.
Ptolemy Journal of Chemistry, 5(1), 202558%
more water held in the outer layer over the same 24 hours
Same study, on a Corneometer CM 825. Hydration rose from 32.4% to 51.2%, p < 0.001.
Ptolemy Journal of Chemistry, 5(1), 2025In people
sunflower seed oil preserved barrier integrity and cut water loss in dry and atopic skin
Human trials of the linoleic acid source in this formula, across dry and atopic skin.
Danby et al. 2012, reviewed in Drug Delivery & Transl. Research 2025
The method
What was measured, on what, by whom.
What was actually measured
Shea butter, the base of this formula, applied at 20 mg/cm² and measured at 1, 2, 4, 8, 12 and 24 hours with a Tewameter TM 300, a Corneometer CM 825 and a conductance meter. Water loss through the surface fell from 8.2 to 5.1 g/m²/h, a 37.8% drop, p < 0.01. Hydration in the outer layer rose from 32.4% to 51.2%, a 58% rise, p < 0.001. Electrical impedance, a proxy for how intact the barrier is, rose 33%.
On what
In vitro, on porcine skin. Pig skin is the standard in vitro stand-in for human skin in barrier work because its lipid structure and thickness are the closest available match. It is not human skin and we are not going to pretend it is. Asher, Angara and Salaudeen, Ptolemy Journal of Chemistry, volume 5 issue 1, 2025.
The human evidence
Sunflower seed oil, the linoleic acid source in this formula, has been trialled topically in people. It preserved stratum corneum integrity and reduced water loss in dry and atopic skin, and it works through PPAR-α, which is a mechanism, not a marketing word. Danby et al. 2012, reviewed in Drug Delivery and Translational Research, 2025.
What this is not
None of the above is a trial of the finished Rü jar. It is evidence about the ingredients this jar is built out of, which is the same class of evidence behind the numbers on almost every premium moisturiser you have ever bought. The difference is that we are naming the papers and the limitation instead of printing a percentage in a big font and hoping you do not ask.
The limits
What we cannot prove yet.
- A panel on the finished jar. The first batch has been in testers' hands for weeks, not months. A number produced from that today would be a number we made up.
- A dermatologist-graded redness or flaking score. Nobody has run one on this cream.
- Verified purchase reviews, because there are no purchases yet.
When the finished-cream panel reads out, its number goes on this page whether we like the number or not, and this paragraph gets deleted.
Until then
60 nights. Use half the jar. Full refund, and keep the jar.
Use it every night for sixty nights. If your skin is not better, email us, keep the jar, and we refund the whole thing. You do not have to send anything back and you do not have to explain yourself.
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