The retinoids are a class of oil soluble compounds related to vitamin A including Retinol, Retinal, Retinoic acid and Retinyl esters. Carotenoids, like Beta Carotene, are sometimes referred to as pro Retinoids since they can be converted into vitamin A by the body.
Retinoids have many important functions in the body including eye health, regulation of cell proliferation/differentiation, bone growth, immune function, and the activation of tumor suppressor genes.
The major dietary sources of retinoids are plant carotenoids and Retinyl esters derived from animal derived foods1. The main form of vitamin A in the body is Retinyl Palmitate, which is converted to Retinol in the small intestine. Retinol is a storage form of the vitamin that and can also be converted to Retinal which is important for eye health2. Retinoids are found in keratinocytes mainly as Retinol and Retinyl esters.
Retinoids are used in the Rx treatment of many dermatological conditions including photodamaged skin (trans Retinoic acid, Tazarotene), Acne (13-cis Retinoic acid, Tazarotene), and Psoriasis (Acitretin, Tazarotene).
The topical Retinoids used in personal care include:
- Retinol
- Retinal
- Retinyl Acetate
- Retinyl Propionate
- Retinyl Retinoate
- Hydroxypinacolone Retinoate
- Retinyl Palmitate
All of these Retinoids - with the exception of Retinyl Palmitate – have been shown to be effective at reducing fine lines and wrinkles, skin roughness, hyperpigmentation, and improving skin texture. Retinoids are believed to work by increasing cell turnover, preventing collagen breakdown, and by thickening the epidermis.
Retinol is the gold standard and one of the top performing skin repair actives currently available. When topically applied, Retinol is oxidized to Retinal, which is further oxidized to trans Retinoic acid. It has been reported that Retinol is ~20 times less potent than trans Retinoic acid due to this extra conversion step.
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Several studies comparing the efficacy of 0.05% Retinaldehyde with 0.05% trans Retinoic acid for the treatment of photoaged skin demonstrated that both Retinaldehyde and trans Retinoic acid were equally effective in reducing wrinkles and skin roughness and are probably more effective than Retinol. However, trans Retinoic acid resulted in a higher incidence of skin irritation than Retinaldehyde3.
To encourage consumer compliance, managing Retinoid-induced skin irritation is important for any new skin repair product. Using polar emollients can reduce irritation by slowing down active release and skin penetration, however this approach probably has a negative effect on efficacy.
Other approaches reported include the use of:
- skin barrier building ingredients (e.g. Niacinamide-Jubilant Life Sciences)
- cosmetic soothing ingredients (e.g. Bisabolol, Dragosantol® 100, Symrise)
- D-Panthenol (BASF Care Creations)
- Dipotassium Glycyrrhizinate (Mafco Worldwide LLC)
- ingredients for making skin less sensitive (e.g. Hydroxyphenyl Propamidobenzoic Acid – SymSitive® 1609, Symrise) (7).
Polar emollients used commercially for irritation reduction include PPG 15 Stearyl Ether (Arlamol PS15E, Croda), PPG-2 Myristyl Ether Propionate (Crodamol PMP, Croda), and sunscreens4.
Another interesting strategy for decreasing irritation and increasing efficacy is to combine Retinol with a Retinol mimic. These mimics claim to modify gene activation in a similar manner to Retinol.
In a published clinical study, .04% Retinol combined with .1% Dihydroxy Methylchromone (DHC-RonaCare Luremin, EMD) and low molecular weight Hyaluronic acid was more effective than .1% Retinol alone at improving photoaged skin8.
Sytenol® A (Bakuchiol-Sytheon) is another reported Retinol mimic that also claims to help stabilize Retinol9. Retinoids reported in the literature as being less irritating than Retinol include Hydroxypinacolone Retinoate (Granactive Retinoid, Grant Industries) and Retinyl Retinoate (k3 Retino-A, Ultra Chemical)5,6.
Stabilizing Retinoids is another important formulation consideration since they easily oxidize, isomerize to a less active form, and are not very photostable.
Stability recommendations (target >90% after one month at 40°C)
- Most Retinoids have optimum stability at a pH of 6-7
- Lamellar gel network based oil in water formulation can help protect against oxidation. Retinol and Retinal can incorporate into the crystalline lamellar phase providing protection against Oxygen.
- Use chelating agents
- Use a combination of oil and water soluble antioxidants
- Avoid using unsaturated emollients and fragrances in the formulation
- Sparge batch making water before using by bubbling Nitrogen into the water until the Oxygen concentration drops below 1ppm.
- Use a package that prevents Oxygen incorporation into the product during use (Aluminum laminate tube). A positive displacement pump may also work.
- Retinoid products applied to skin during the day should contain SPF and or photostabilizers.
Commercially available Retinoids
- Vitamin A Palmitate 1.7 MIU/g (Retinyl Palmitate-DSM Nutritional Products)
- Retinol 15 D (Caprylic/Capric Triglyceride (and) Retinol-BASF Care Creations)
- RetiStar Stabilized Retinol (Caprylic/Capric triglyceride (and) Sodium Ascorbate (and) Tocopherol (and) Retinol-BASF Care Creations)
- Retinol 50 C (Retinol (and) Polysorbate 20-BASF Care Creations)
- PromaCare VAA (100MIU G) (Retinyl Acetate-Uniproma Personal Care Division)
- Granactive Retinoid (Dimethyl Isosorbide (and) Hydroxypinacolone Retinoate-Grant Industries) – claimed to be less irritating than Retinol and effective without needing to be metabolized to Retinoic acid
- k3 Retino-A (Retinyl Retinoate -Ultra Chemical) - claimed to be more photo and heat stable than Retinol. A clinical study using 0.06% Retinyl Retinoate cream for three months showed decreased depth and area of wrinkles similar to 0.075% Retinol cream. Skin roughness also improved more than the Retinol cream.
- All-Trans-Retinal (Retinal-Spectrum Chemical Mfg. Corp.)
References
- https://en.wikipedia.org/wiki/Retinoid
- https://en.wikipedia.org/wiki/Vitamin_A
- Retinoids in the treatment of skin aging: an overview of clinical efficacy and safety
- Topical oil-in-water emulsions containing retinoids-US 5976555, Johnson and Johnson, 11/2/99
- k3 Retino-A (Retinyl Retinoate-Ultra Chemical) supplier brochure
- Granactive Retinoid (Dimethyl Isosorbide (and) Hydroxypinacolone Retinoate-Grant Industries) supplier brochure
- Draelos ZD, Ertel KD, Berge CA. Facilitating facial retinization through barrier improvement. Cutis. (2006).
- Oddos T, Roure R, Leyden J, Bruère V, Bertin C,. A Placebo-Controlled Study Demonstrates the Long-Lasting Anti-Aging Benefits of a Cream Containing Retinol, DihydroxyMethylChromone (DMC) and Hyaluronic Acid. Journal of Cosmetics, Dermatological Sciences and Applications, 2012, 2, 51-59.
- Stenol A (Bakuchiol-Sytheon) supplier brochure.
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George, Great job summarizing Retinoids with regard to their use, functionality, application and availability.
George, this is yesterday’s news. Retinoids have been replaced with far safer methods of treating dry and damaged skin. Today’s best offerings for treating wrinkles are more organic and naturally based and they include stem cells and peptides among others.
There is too much evidence of retinoid abuse over time and too many examples of unwanted side effects from the overuse of retinol.
Let’s move on with the times.
George – Nice summary of the efficacy of retinol as the gold standard in skin care.
I noticed that you also had a number of strategies for improving stability and reducing irritation however, microparticle delivery systems where not discussed. These systems can address both stability and irritation. An All-Natural microparticle delivery system for retinol is also available.
Lastly, when discussing stability of retinol, you did not mention that most retinols are stabilized with BHA which is listed on CA Prop-65. It would be advisable to look for BHA-Free products when formulating with retinol.
I look forward to reading more.
Retinoids are the best (scientific prove) treatment out of any doubt.
Steam cells the most effective, really? With all the due respect, you should review the human skin structure and a little bit of basic biology.
You do realize that stem cells needs to be alive in order to do anything? Stem cells in cosmetics are NOT alive, they’re dead. Furthermore, they typically use plant stem cells in cosmetics so they can’t do anything for human skin. But by all means continue using them and let me know if you start growing branches.