How retinaldehyde, retinol and tretinoin compare on irritation

This study did two things. In a small 14-day patch test on six people, retinol and retinaldehyde came out equally low in irritation, while retinoic acid was significantly more irritating — although both retinaldehyde and retinoic acid produced more scaling than retinol. Six people is far too few to settle whether retinal is as gentle as retinol, and that question remains open. The larger and more useful part followed 355 people using either retinaldehyde or retinoic acid for 44 weeks. In the first four weeks on retinoic acid, 44% had redness, 35% scaling, and 29% burning or itching. All three were significantly less frequent with retinaldehyde. This is the clearest evidence for the central claim made about retinaldehyde: that it gives you a retinoid effect with far less of the early irritation that makes people abandon tretinoin.