Retinol and tretinoin are both Vitamin A derivatives. They are naturally occuring substances that are found in meat, poultry, eggs and dairy products. Our bodies cannot make vitamin A, so we depend on outside sources for it. Retinol is the precursor of tretinoin, also known as retinoic acid. Both retinol and tretinoin can improve skin tone and texture. Both induce important proteins and cellular mechanisms that promote healthy, supple skin, and both are able to block the damaging effects of ultraviolet rays.
However, retinol is 20 times less potent than tretinoin and must undergo several conversion steps before it becomes pure tretinoin. This makes retinol weaker than tretinoin but generally less irritating. This also makes retinol less stable than tretinoin and more prone to degradation upon exposure to light and air- this is especially important in topical products, where the base can vary considerably. Tretinoin is much more stable and can be used in a variety of bases, depending on the specific formulation. Both tretinoin and retinol improve skin quality after 12 weeks of use, but tretinoin has been shown to be more effective for fine lines and wrinkles. See study here.