Which form of retinoids should one choose?

Prescription retinoids, often grouped under the name of retinoic acid or vitamin A acid, are the most active forms of this family of molecules. Their use is primarily reserved for the management of moderate to severe acne, but they can also be prescribed for certain signs of skin photoaging or keratoses. There are three main forms of retinoids used in dermatology:

• Tretinoin, or all-trans-retinoic acid, is often formulated at concentrations ranging from 0.025% to 0.05%, either alone or combined with a local antibiotic, such as erythromycin.

• Isotretinoin, also known as 13-cis-retinoic acid, can be used topically, often in combination with erythromycin, or more commonly taken orally to combat severe or persistent acne.

• Adapalene, a new generation molecule, which can be prescribed alone or in combination with benzoyl peroxide, an antiseptic agent known for its action on Cutibacterium acnes, the bacteria involved in the pathogenesis of acne.

Retinoic acid operates on several fronts to reduce imperfections and mitigate the signs of photoaging. Unlike most other forms of retinoids, it is active in the epidermis and does not require conversion. Retinoic acid interacts directly with retinoic acid receptors (RAR) and retinoid X receptors (RXR), thereby triggering a cascade of cellular signals that lead to the stimulation of epidermal renewal and the activity of fibroblasts, the cells synthesising the various compounds of the extracellular matrix (collagen, elastin, glycosaminoglycans such as hyaluronic acid...).

However, this high efficacy of retinoic acid comes with a strong potential for irritation. Redness, peeling, dryness, burning sensation... adverse effects are common, particularly at the start of treatment, if the skin barrier is weakened or if too much product is used. That's why retinoic acid is not used in skincare and is strictly dispensed on medical prescription. Its use requires dermatological supervision to adjust the dosage, prevent side effects and choose the right form based on the skin typology and the patient's needs.

Three forms of retinoids are available on the cosmetic market and do not require a prescription. Even though these molecules cannot combat severe acne, they can reduce blemishes and help fight against signs of ageing (wrinkles, fine lines, skin sagging). The retinoids usable in cosmetics are:

• Retinol, for mature or acne-prone skin that is not sensitive.

  The most popular retinoid in skincare, retinol is regarded as one of the most effective compounds to counteract the degradation of the skin's support fibres by stimulating the production of collagen and elastin. Moreover, it is recognised for its antioxidant properties that prevent premature ageing of skin cells by combating oxidative stress. The retinol also has an effect on the skin's melanin production, helping to reduce the appearance of brown spots that can emerge with age. Generally recommended for mature skin, retinol is also a top choice for acne-prone skin. Although it doesn't have a keratolytic action per se, its ability to accelerate the skin's cell renewal prevents pore blockage and the emergence of blemishes, such as blackheads for instance.

  Note : Although retinol is generally recommended for mature skin, it can be used from your twenties as a preventative measure against wrinkles. However, it is advised to start with a low percentage of retinol, for instance, a product with a concentration of 0.01% or 0.05%. It's worth mentioning that the maximum concentration of retinol in a non-rinse cosmetic formula is limited to 0.3% by European Regulation.

• Retinal, also recommended for mature or acne-prone skin that is not sensitive.

  From a chemical perspective, retinal is a metabolite that sits between retinol and retinoic acid. Indeed, when applied to the skin, retinol is oxidised into retinal and then metabolised into retinoic acid, its active form that effectively combats photoaging, blemishes, and hyperpigmentation. Thus, retinal is more directly converted into retinoic acid in the skin than retinol. Closer to the active form than retinol, retinal is generally considered more potent than the latter but not necessarily more irritating. This form of retinoid can therefore have a smoothing and regenerating action at lower concentrations, ranging between 0.015% and 0.1%.

• Retinoid esters, for initial wrinkles, minor blemishes, and sensitive skin.

  More stable than retinol and retinal, retinoid esters are also gentler on the skin. The most commonly used are retinyl acetate (INCI: Retinyl Acetate), retinyl propionate (INCI: Retinyl Propionate), retinyl palmitate (INCI: Retinyl Palmitate) and retinyl linoleate (INCI: Retinyl Linoleate). They are easily identifiable by their "ate" suffixes. However, retinol esters are often less effective on wrinkles and blemishes than retinol or retinal, as they must undergo more transformations in the skin before taking the form of retinoic acid. These retinoids are nevertheless relevant if you have sensitive skin but still want to start incorporating vitamin A derivatives into your skincare routine.

Note : To combine efficiency and tolerance, skincare brands are exploring new active ingredients, such as the hydroxypinacolone retinoate. This next-generation retinoid, although an ester, binds directly to the retinoic acid receptors without enzymatic conversion, thus combining performance and high tolerance.

• MUKHERJEE S. & al. Retinoids in the treatment of skin aging: An overview of clinical efficacy and safety. Clinical interventions in aging (2006).

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

• BAE J. M. & al. Efficacy and safety of retinaldehyde 0.1% and 0.05% creams used to treat photoaged skin: A randomized double-blind controlled trial. Journal of Cosmetic Dermatology (2018).

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

• YE R. & al. The synergistic effect of retinyl propionate and hydroxypinacolone retinoate on skin aging. Journal of Cosmetic Dermatology (2023).