Retinal
One conversion step from retinoic acid; faster-acting than retinol in the few trials that exist, with good tolerance.
Retinal (retinaldehyde) is the intermediate between retinol and retinoic acid. Because only one oxidation step remains, it is often marketed as "eleven times faster" than retinol; the number comes from in-vitro conversion kinetics rather than a clinical race.
The evidence
An 18-week comparison of 0.05 % retinaldehyde and 0.05 % retinoic acid found both improved wrinkle profilometry, with retinaldehyde tolerated as well as vehicle[2]. Earlier work established that it produces retinoid-type biological effects in human skin without the irritation profile of retinoic acid[1]. There is also laboratory evidence of direct antibacterial activity[3], which is why it appears in some acne-adjacent products.
The catch is volume: the literature is a fraction of retinol's, which keeps the grade at Moderate.
Evidence by claim
Safety & limits
Sources · 3
- [1]Saurat JH, Didierjean L, Masgrau E, et al.. Topical retinaldehyde on human skin: biologic effects and tolerance. Journal of Investigative Dermatology (1994)doi:10.1111/1523-1747.ep12395611
- [2]Creidi P, Vienne MP, Ochonisky S, et al.. Profilometric evaluation of photodamage after topical retinaldehyde and retinoic acid treatment. Journal of the American Academy of Dermatology (1998)doi:10.1016/S0190-9622(98)70590-8
- [3]Pechère M, Germanier L, Siegenthaler G, et al.. Antibacterial activity of retinaldehyde. Dermatology (2002)doi:10.1159/000067820