Types and strengths of retinoids
Recall that retinoids are a class of ingredients. The most important types of natural retinoids are listed below, going from the strongest to the weakest: [1] [2] [3]
Retinoic acid (tretinoin)
Retinoic acid is the most potent form of retinoid available that is also known by the name tretinoin or its brand name Retin-A. It is the only retinoid that the skin can use directly.
Retinaldehyde
Retinaldehyde, also known as retinal, is a less potent form of retinoid than retinoic acid. It is converted to retinoic acid by the skin before it can be used.
Retinol
Retinol or vitamin A is the least potent form of retinoid. It is converted to retinaldehyde and then to retinoic acid by the skin before it can be used. Retinol is often used in over-the-counter anti-aging products.
To summarise, retinoic acid is the most potent form of retinoid, while retinaldehyde and retinol are less potent. Retinoic acid can be used by the skin, while retinaldehyde and retinol need to be converted to retinoic acid by the skin before they can be used.
Note that the retinoids listed above are known as natural retinoids. There are also synthetic retinoids that try to mimic certain effects of natural retinoids without having the same side effect profile: [4]
Adapalene
Adapalene is a synthetic retinoid that has a similar potency to tretinoin while being less irritating. Because adapalene has not been around as long as tretinoin, there is less research on its long-term anti-aging effects. However, the studies that do exist show that it is just as effective as tretinoin.
Tazarotene
Tazarotene is another synthetic retinoid that is more potent than tretinoin. Just like adapalene, tazarotene aims to mimic the effects of natural retinoids without being as irritating. It has also been studied less than tretinoin, but studies do show that it is more effective than tretinoin.
