Retinoids: retinal, retinol and the rest

The conversion ladder

All cosmetic retinoids work by becoming retinoic acid, the form that binds nuclear retinoic acid receptors. The difference between them is how many enzymatic steps that takes. Retinyl esters convert to retinol, retinol to retinal (retinaldehyde), retinal to retinoic acid. Each step loses efficiency, so fewer steps generally means more activity at the same concentration — and usually more irritation.

Retinal sits one step from retinoic acid, which makes it substantially more potent than retinol at equal concentration while remaining a cosmetic rather than a pharmaceutical ingredient in most jurisdictions.

Levels that mean something

Retinoid concentrations are small and the units matter. The Youlief Cica Retinal Ampoule states retinal at 100 ppm, which is 0.01%. That is a genuine functional level for retinal and consistent with the range used in published work — worth contrasting with the many ingredients in cosmetic ranges present at a thousandth of that.

Retinol products typically run 0.1% to 1%. Comparing a retinol percentage directly against a retinal percentage is misleading, because of the conversion difference.

Why formulation is most of the problem

Retinoids oxidise on exposure to air, light and heat, and the degradation products are inactive. A poorly formulated retinoid is not a weak retinoid, it is an absent one. This is why encapsulation, opaque airless packaging and antioxidant systems matter more here than for almost any other active — and why the presence of hydrogenated phosphatidylcholine and lecithin alongside retinal in the Cica Retinal Ampoule is worth noting: those are liposome-forming materials, consistent with a protected delivery approach.

Tolerance, and what actually helps

Irritation, flaking and transient worsening are common in the first weeks and are dose- and frequency-dependent rather than a sign the product is working. Building up frequency, applying to dry skin, buffering with a moisturiser and pairing with barrier support all reduce it. Retinoids increase photosensitivity in practice, so evening use and daytime sun protection are not optional.

What does Retinoids: retinal, retinol and the rest not do?

They do not work quickly — meaningful change in fine lines and texture takes months, not weeks. They do not exfoliate, despite the flaking. And they are not appropriate in pregnancy: topical retinoid use should be discussed with a clinician, and the conventional advice is to avoid it.