Octadecenedioic Acid
Explained
This ingredient is also known as dioic acid and it's basically azelaic acid's cousin. They're part of the same dicarboxylic acid family and dioic acid is longer with 18 carbons instead of 9.
Like azelaic acid, dioic acid is great with lifting dark spots. But instead of blocking the pigment enzyme tyrosinase directly, it switches on receptors in the skin cell that tells the cell to make less tyrosinase in the first place.
Lab tests confirm its ability to tell cells to make less of the pigment-building enzyme and affected the "recipe" for it as well. So less melanin came out in both cells and on actual skin.
On real people, a 12-week study on 96 women with melasma compared 1% dioic acid cream twice daily against 2% hydroquinone. Both performed comparatively at brightening skin and the only difference is that itching was more common in the hydroquinone group.
A separate 12-week study in 71 women used used 1% dioic acid alongside 2% Rumex occidentalis extract and SPF 15. They results showed a significant lightening versus the participant's own baseline at weeks 4, 8, and 12.
Usage concentrations land at roughly 1-2% in published clinical work, though suppliers sometimes push 2-4%.
This ingredient isn't a recognized contact allergen and has been found safe at current use levels/concentrations by the CIR Expert Panel.
Though tolerance in the trials were found to be good, a small number of people may find it irritating (as with any acid).
See all 44 products with Octadecenedioic Acid
