Retinal (also known as retinaldehyde) behaves in a similar way to the better known retinol, but it is much more stable and more effective. When vitamin A is not being used by the body, it is stored within the skin cells as retinyl esters. Once the body is ready to metabolise vitamin A, these esters are converted to retinol, and then to retinaldehyde before ultimately becoming retinoic acid.
Retinoic acid is the active form of vitamin A, the form that is actually utilised by the skin. That’s why all variations of vitamin A, including retinol and retinal, must be converted to retinoic acid before they can take effect. This means that when retinal and retinol are applied to the skin, they join the vitamin A cycle at their respective stages. retinol must be converted to retinal and then to retinoic acid, whereas retinal only requires one conversion to retinoic acid. Crucially, this last step is extremely rapid compared to the previous conversions which is why retinal is able to provide such rapid results (up to 11 times faster).