Here's what you need to know about retinol.

The retinol belongs to the family of retinoids and is, along with retinoic acid and retinal, one of the three available forms of vitamin A. Its history can be traced back to ancient Egypt, where beef liver compresses, containing retinol, were used to treat blindness, hence its name derived from the "retina" of the eye. However, it was not until 1931 that the retinol molecule was first isolated by Swiss chemist Paul KARRER, from mackerel liver oil. The effectiveness of this organic compound on signs of ageing was then demonstrated in the 1980s by American dermatologist Albert KLIGMAN.

The retinol is widely used in skincare today, whether in serums, moisturisers, cleansing gels or even eye contour treatments. In Europe, its concentration in non-rinse products is limited to 0.3% by Regulation (EC) No 1223/2009 of the European Parliament and of the Council. It's worth noting that retinol is not biologically active. After application to the skin, it undergoes two successive enzymatic conversions, first into retinal, then into retinoic acid. It is this latter compound that is biologically active.

Retinol can be obtained through chemical synthesis. There are several methods to produce retinol, but most often, the synthesis begins with the reaction of β-ionone with a propargyl halide, in the presence of a metal such as zinc or a magnesium/mercury amalgam. Through a Grignard-type reaction with an acetal-protected reagent, an alkyne compound is obtained, which is then reduced by hydrogenation using a palladium or Raney nickel catalyst.

A dehydrating agent, such as PCl₃, POCl₃, BF₃, AlCl₃ or PCl₅, is then used to form a conjugated polyene. The subsequent acid treatment has a dual effect: it removes the protection of the enolic ether and reorganises the double bonds, giving rise to an aldehyde. A final migration of the double bonds is induced by a basic catalyst, such as pyridine, soda or isopropyl aluminate [Al(OiPr)₃]. Finally, the vitamin A aldehyde can be reduced to vitamin A using various reducing agents, such as LiAlH₄ or Al(OiPr)₃.

The retinol is one of the most utilised molecules in skincare for maintaining skin health. Indeed, it has numerous skin benefits:

• Retinol assists in evening out the skin tone.

  Once converted into retinoic acid, retinol acts on keratinocytes by activating the nuclear receptors RAR (Retinoic Acid Receptors), which induces an increased proliferation of the basal cells of the epidermis. This faster renewal allows for more regular desquamation and the removal of cells from the horny layer loaded with melanin or oxidised, contributing to a more even and luminous complexion.

• Retinol has a preventive and corrective effect on signs of ageing.

  The retinoids can also stimulate the expression of genes involved in the synthesis of type I and III collagen and elastin, while inhibiting the enzymes responsible for their degradation, including certain matrix metalloproteinases. Their ability to stimulate cell renewal also plays a role in reducing wrinkles and fine lines.

• Retinol assists in reducing hyperpigmentation.

  Retinoids, such as retinol, are also a good option for brown spots. Their depigmenting effects are thought to come from their ability to accelerate the cellular renewal of the epidermis, allowing for a quicker differentiation of keratinocytes from the basal layer to the horny layer and a faster loss of melanin via epidermopoiesis. It is also suggested that retinoids could lead to a uniform dispersion/distribution of melanin granules in the keratinocytes.

  Note : Contrary to some misconceptions, retinol is suitable for all phototypes, including dark skin.

• Retinol shields the skin from oxidative stress.

  The numerous conjugated double bonds of retinoids allow them to stabilise free radicals, reactive compounds that are particularly generated following exposure to the sun or pollution. They thus combat oxidative stress, which is harmful to the skin as it can cause inflammation, accelerate skin sagging, and promote pigmentation issues.

• Retinol promotes the removal of blemishes.

  By normalising the keratinisation of the pilosebaceous follicle, retinoids prevent the accumulation of corneocytes and the formation of keratin plugs, an action beneficial for preventing blackheads. They are also attributed with a seborrheic action. However, although this activity has been demonstrated in vitro and is widely documented for oral retinoids, clinical evidence regarding topical retinoids remains limited.

Even though this use of retinol is less common, this molecule can also be used to care for hair, particularly the scalp. Indeed, by promoting cell renewal and encouraging the normalisation of desquamation, retinol accelerates the elimination of cells from the stratum corneum. This can be particularly relevant for individuals prone to dandruff. Let's remember that dandruff forms following the agglomeration of epidermal cells which then detach in white clusters.

Some studies also suggest that retinol could potentiate the effects of minoxidil, a medication used in androgenetic alopecia. In 2007, a study in vitro tested this combination on human hair follicles incubated for 12 days. The researchers compared the growth achieved with minoxidil alone (1 µM) to that observed with the addition of retinol (17 nM). Significantly greater hair growth was measured for the combination group. Other studies report comparable effects, contributing to the idea that retinol promotes hair growth. However, this hypothesis remains to be nuanced, as no work has yet evaluated the effect of retinol alone on hair growth.

Retinol and retinoids in general are often criticised for their potential irritant properties and associated side effects such as redness, tingling sensations, and peeling. This is why they are generally not recommended for sensitive skin. These drawbacks related to retinoids are explained by their mode of action. By activating cell renewal, these molecules can temporarily alter the skin barrier and cause an increase in transepidermal water loss as well as skin sensitivity. To limit these side effects, some cosmetic brands now offer encapsulated retinoids or gentler next-generation retinoids, such as hydroxypinacolone retinoate.

Before using a retinol-based treatment, we advise you to perform a skin tolerance test. Apply a few drops of the product in question to the crook of your arm or on your wrist and wait 24 to 48 hours. If you observe a significant skin reaction, do not apply the treatment to your face. However, it should be noted that the skin may require an adjustment period when introducing a retinoid into its care routine. That's why it's often recommended to start with a low concentration of retinol. In case of very slight redness, you can try to space out the applications every other day or every three days. However, if the erythema persists, you should stop using the product.

Finally, retinol is a molecule that is used in the evening and requires the application of sun protection the following morning. Indeed, the numerous conjugated double bonds present in the chemical structure of retinoids make these compounds sensitive to photochemical reactions. When exposed to sunlight, they are likely to transform into reactive intermediates that can damage the skin.

The use of retinoids, whether oral or topical, is strictly contraindicated during pregnancy and breastfeeding.

You can find retinoids in several of our treatments at Typology.

• The retinol serum for fine lines and wrinkles: Concentrated at 0.3% retinol, this treatment containing 99% natural origin ingredients aids in preventing skin sagging by stimulating the synthesis of collagen and elastin, for smoother skin. The fine lines and wrinkles serum also contains castor oil and soybean oil, ideal for nourishing mature skin.

• The firming night cream: With 0.2% retinol and tsubaki oil, this night cream is enriched with tightening agents to slow down the appearance of wrinkles and make the skin more plump. It contains 98% naturally derived ingredients and boosts the production of collagen and elastin fibres, in order to prevent signs of skin ageing.

• The eye serum for fine lines and wrinkles: This serum formulated for the sensitive eye contour area contains 0.1% hydroxypinacolone retinoate, a mild retinoid that acts directly on RAR receptors, for enhanced efficacy on wrinkles and sagging skin. This serum also contains hyaluronic acid, known for its moisturizing properties, and niacinamide, soothing and protective.

• KAFI & al. Improvement of naturally aged skin with vitamin A (retinol). Archives of Dermatology (2007).

• Règlement (CE) No 1223/2009 du Parlement Européen et du Conseil.

• KIM K. H. & al. The Additive Effects of Minoxidil and Retinol on Human Hair Growth in Vitro. Biological and Pharmaceutical Bulletin (2007).

• LIN C. B. & al. A novel anti-ageing mechanism for retinol: induction of dermal elastin synthesis and elastin fibre formation. International Journal of Cosmetic Science (2011).

• BAXENDALE I. R. & al. Development of the industrial synthesis of vitamin A. Tetrahedron (2016).

• QUAN T. & al. Molecular basis of retinol anti-ageing properties in naturally aged human skin in vivo. International Journal of Cosmetic Science (2017).

• ZASADA M. & al. Retinoids: active molecules influencing skin structure formation in cosmetic and dermatological treatments. Advances in Dermatology and Allergology (2019).