15% is not a random number. Partnered with skinceuticals on the new C E Ferulic, the formula's first update in over 20 years. #ad The Duke Parameters come from the original research: pure vitamin C absorbs best between 10 and 20 percent, at a pH under 3.5. Above 20, absorption drops. More is not better, formulated is better. The new clinical testing showed improvement across 8 signs of aging, in all skin tones and men. That should be the default. It still isn't. Decade club: how long has the original been in your routine? #skinceuticals #VitaminC #longevity