Both are forms of Vitamin A, but they differ in how many conversion steps the skin needs before the ingredient becomes active retinoic acid.
Retinol requires two conversion steps; retinal (retinaldehyde) requires only one — meaning it works faster and, in clinical comparisons, with less irritation at equivalent strength. That’s why we formulated our Renewal Serum around 0.1% retinal rather than a traditional retinol.
As with any Vitamin A derivative, start two to three nights a week and always follow with SPF the next morning.