What is the difference between retinol and retinoids?

Retinoids is the umbrella term for all vitamin A derivatives, including prescription-strength tretinoin, retinaldehyde, and over-the-counter retinol. Retinol must be converted by the skin into retinoic acid before it is active, which makes it gentler but also less immediately potent than prescription tretinoin. Prescription retinoids work faster and more dramatically but carry a higher risk of irritation.