The mildest vitamin A form. It needs three conversion steps to become active, so it is gentle but weak; mostly found in lotions at low levels, where it does more for the label than for the skin.
Retinyl palmitate is retinol bound to a fatty acid — the form skin uses to store vitamin A. To act it must be cut back to retinol, then oxidized to retinaldehyde and retinoic acid. That makes it stable and non-irritating, and also much weaker: in a human-skin comparison it took about 0.6% retinyl palmitate under occlusion to match the effect of 0.025% retinol, and uncovered it performed worse.
It appears in body lotions, foot creams and eye creams, usually at unstated low levels. Retinyl propionate is a similar ester. A lotion that lists just "vitamin A" most often contains one of these esters, but the label doesn't say which.
Human data are mostly penetration and skin-marker studies; controlled trials showing visible wrinkle improvement from retinyl palmitate alone are scarce. A mouse study raised concern that it might speed UV-induced tumours when used in sunscreen; a critical review judged that the data do not show a risk to people.
On human skin under occlusion, about 0.6% retinyl palmitate, 0.025% retinol and 0.01% retinaldehyde were needed to produce a measurable retinoid effect; without occlusion, retinyl palmitate did less well while retinol worked as well as when covered.
Examined the mouse photocarcinogenicity data behind claims that retinyl palmitate in sunscreens promotes skin cancer, and concluded the evidence does not show such a risk in people.