For decades, skin care professionals have been aware that compounds derived from vitamin A, known as retinoids, have beneficial effects on ageing skin. The early retinoid compounds were highly effective but had harsh side effects. They often left skin feeling dry, flaky and irritated. Through continued research and development, dermatologists refined the available retinoid compounds until they produced a variant that delivered measurable anti-ageing benefits, yet was gentle enough not to irritate skin. The result of their labours was retinol, a retinoid that can be used on all skin types.