Well, hello again! We know that the topic related to retinoids is extremely important, yet
extensive, so please stay patient with us as we continue our conversation. If you haven't read
Part I “The Inescapable Reality of Retinoids”, make sure you do
so!
The Science and Functionality Behind Retinoids
The science behind how retinoids work is very intricate. In a nutshell, “they bind to retinoic acid receptors in the nucleus of skin cells and activate gene expression”[1], which reciprocally triggers a variety of skin responses.
Such skin responses include, but are not limited to:
1. Blood flow enhancement [2]
2. Cell regeneration which results in smoother and plumper skin as new skin cells rebuild the outermost layer of the skin[2]
3. Firmer skin as a result of collagen and elastin boost. These proteins are responsible for strengthening the fibers that bind the epidermis and dermis together[2]
4. Discoloration of the skin is minimized due to the decrease in the amount of melanin (skin pigment) produced by the melanocytes[2]
5. Increase in the hydration levels within the skin as a result of the production of glycoproteins such as hyaluronic acid[3]
6. Inflammation is reduced[4]
7. Complexion is clear up due to the reduction via exfoliation of abnormal keratin production that causes all forms of acne as well as keratosis pilaris (or chicken skin)[4]
8. Excessive skin shedding as a result of psoriasis is reduced and normalized[1]
9. Control of sebum output[5]
10. Pore size minimization[3]
What Are The Different Categories Of Retinoids?
You have probably seen a number of different types of retinoids and are wondering what the differences are, well, we summarized the differences for you below:
- First generation: these are the natural retinoids —although nowadays they are mostly produced synthetically— including: retinoic acid, retinal, retinol and their esters (derivative produced by the reaction of an acid and an alcohol). You will usually find the prefix all-trans being used as part of their name. The next generations are all synthetic[6] [7].
- Second generation: acitretin and etretinate[6] [7].
- Third generation: arotinoid, adapalene, bexarotene and tazarotene[6] [7].
- Fourth generation: seletinoid G and trifarotene[8]
The Definition Of The Retinol Conversion Chain
▪ Before retinoids can bind to retinoic acid receptors they need to be converted or oxidized by enzymatic action to —yes, you guessed it— retinoic acid.[6] [7] This is the bioactive form of vitamin A[6] [7] .
▪ The less conversions a retinoid has to undergo, the more effective and potent it is[6] [7] .
▪ From top to bottom, this is how the retinoid conversion chain looks like:
- Retinoic acid (Tretinoin or Retin-A), Hydroxypinacolone Retinoate (Granactive retinoid)* as well as all the second, third and fourth generation retinoids** [6][7] [9][10].
- Retinaldehyde (Retinal), Retinyl retinoate*** [6][7] [9][10].
- Retinol [6][7] [9][10].
- Retinol esters: retinyl acetate, retinyl linoleate, retinyl palmitate and retinyl propionate.[6][7] [9][10]
*Hydroxypinacolone retinoate is an ester of retinoic acid that binds directly to the retinoic acid receptors without having to be oxidized.[10] This retinoid is much more stable and has less irritation potential than retinol, retinal and tretinoin[10].
** Second, third and fourth generation retinoids: they have retinoic acid-like activity, so they also bind directly to the receptors[7]. These compounds are classified as prodrugs, so most of them can elicit very strong reactions and require a prescription.[7]
*** Retinyl retinoate: it is an ester of retinoic acid and retinol[11]. So, one part will only undergo one conversion to retinoic acid and the other one will be converted first to retinol and then to retinoic acid.[11]
We know we might have gotten a bit too technical with our terminology; however, this information is extremely important when you purchase your next skin care products! We still have a few more tips and tricks to tell you about, stay on the lookout for our last blog post about “The Dark Side Of Retinoids- Part III”.
References:
[1] https://www.aocd.org/page/Retinoidstopical
[2] https://www.dermcoll.edu.au/atoz/retinoids/
[4] https://www.dermatologytimes.com/view/better-safety-profile-new-retinoid-development
[5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5605215/
[6] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6791161/
[7] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2699641/
[8] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7558148/
[9] https://aem.asm.org/content/82/13/3940
[10] https://www.jaad.org/article/S0190-9622(18)31012-0/fulltext
