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What are retinoids and retinols?

I presume you’re reading this because you are aware of all the great things retinoids and retinols can do for your skin, but are confused over the terminology. This is where a PhD in organic chemistry comes in handy. Let me deconstruct their differences and why it matters.

Retinoid and retinol are different but also the same. Huh? Let me explain. Often, Retinoid is used as an umbrella term for any compound derived from vitamin A (a vitamin A derivative). A vitamin A derivative possesses structural or functional similarities to vitamin A, but is not quite vitamin A. In some contexts, the term retinoid can also refer to prescription-strength vitamin A derivatives (such as tretinoin and tazarotene).

It turns out that vitamin A and retinol are actually the same compound (they are just two different names for the same thing). Thus, retinol and any vitamin A derivatives you can think of – retinal (aka retinyladehyde or retinaldehyde), adapalene, retinoic acid, retinyl esters (such as retinyl propionate and retinyl palmitate), tretinoin and tazarotene – can be classified as a retinoid. Despite retinol not being a vitamin A derivative, but vitamin A itself, it is generally still considered a retinoid.

How do the different types of retinoids differ?

As I’ve alluded to above, vitamin A and retinol (aka all-trans-retinol) are technically the same compound (see below).

However, retinol is not the most active form of vitamin A (if we want amazing skin). When we use retinoid products in the pursuit of perfect skin, it is not vitamin A (retinol) we can thank for this, even if retinol is the only retinoid in the product. For the most part, retinoic acid (all-trans-retinoic acid) is actually the compound producing the effects we want. So there has to be some chemistry going on once we apply these products, in order to produce retinoic acid (see below).

So how do skincare products with only retinol as the active ingredient end up forming retinoic acid when applied to our skin?

Retinol is converted to retinoic acid in two steps: firstly, alcohol dehydrogenase (ADH) or retinol dehydrogenase (RDH) enzymes catalyse the oxidation of retinol to retinal. The reverse reaction may also occur. Subsequent oxidation of retinal by retinaldehyde dehydrogenases (RALDH – of which there are several types) furnishes retinoic acid (this is an irreversible step).

With retinyl esters, these are first converted to retinol, which then undergoes the same two-step process as above. Or, as you can imagine, retinals only have the one step to go through to produce retinoic acid.

How does retinoic acid work?

So now we know the key to reduction in fine lines and acne, cell renewal and collagen production (click here to read why collagen is so important as an anti-ageing product) is retinoic acid…. how does it work?

Retinoic acid seeks to activate the three retinoic acid receptors (alpha, beta, gamma). Since it is a lipophilic molecule, it can diffuse through cellular and other phospholipid membranes. Once retinoic acid has bound to its receptors, inside the cells, modulation of gene (genes involved in cellular differentiation and proliferation) expression occurs. This results in the reduction of fine lines and acne, cell renewal, collagen production and more. Everything we have come to expect of retinoids.

Whilst the known ligand for retinoic acid receptors is retinoic acid, which is why retinoic acid is the biologically active species, studies have shown other retinoids may be capable of binding to these receptors. Retinol was found to bind to all three retinoic acid receptors (alpha, beta, gamma), however to a much lesser extent (4–7-fold lower affinity). Importantly, it was not a result of the metabolism of retinol to retinoic acid. Retinal showed very little interaction with the receptor, whilst Retinyl acetate (another retinyl ester) was virtually inactive. So although retinoids such as retinol, retinal and retinyl esters are likely to take effect via conversion to biologically active retinoic acid, we cannot rule out a direct interaction of these retinoids with the retinoic acid receptors.

In addition to binding to nuclear receptors, there is evidence that the spectral properties of retinoids make them efficient in preventing UVB-induced apoptosis and DNA photodamage. A study showed that the application of topical retinyl palmitate 2% was as efficient as SPF 20 sunscreen.

Which retinoids should I use?

When thinking about which retinoid to use there are several factors you should consider: the sensitivity of your skin, UV stability of the product, whether you are pregnant/breastfeeding.

Sensitive skin

If you have sensitive skin don’t go for prescription retinoids – start with something less potent such as retinol etc. Since retinol (retinal and retinyl esters too) has to be first converted to retinoic acid, the concentration of retinoic acid at any one time is much lower and thus less irritating. Taking this even further, a lower concentration of any retinoid is always better for sensitive skin. It will take a little longer to see results from using retinol compared to retinoic acid, but will be all that most people require to see some good results.

UV stability

Although UV light stability of retinoids vary, retinol (perhaps the most widely used in anti-ageing products) is very unstable in the presence of UV light. Therefore formulation and packaging are very important when it comes to these anti-ageing products. It’s all well and good if these products technically contained retinol at a certain point in time, but due to poor formulation and/or packaging, the resultant product might be mostly garbage by the time you come to use it. Or perhaps after a few uses.

Exposure of the formula to light and air will result in loss of potency of the product. Thus, make sure to look for dark amber glass containers or opaque tubes. Also airtight pumps are great! Preservatives also play a large role – butylated hydroxytoluene (BHT) is a common antioxidant preservative. The product could also come in the form of a serum, cream or gel. These all affect a product’s efficacy.

Pregnancy

If you are pregnant or breastfeeding then you should not be using retinoids. Ingestion of retinoids whilst pregnant is known to cause birth defects. Although there is likely to be minimal systemic absorption of retinoids used topically, it is not advised to use retinoids whilst pregnant or breastfeeding.

For those who are pregnant or breastfeeding, bakuchiol has been shown to stimulate collagen production, whilst being more gentle on the skin. Though, since there are few studies on the safety of bakuchiol, it is advised not to use it during pregnancy or when breastfeeding. But, it may be a good option for those who don’t get along with retinol because of sensitive skin.

Side effects

Initially you might experience redness, peeling, and overall irritation as your skin gets used to the ramped-up cell turnover. So it is always best to start off slow and perhaps use a retinoid every 2-3 days whilst your skin acclimatises (even now, my sensitive skin certainly can’t tolerate daily use). It’s also best to use retinoids at night – although some studies hint at retinoids offering some UV protection (please do not use retinoids as a form of sun protection) – retinoids may produce deleterious effects upon photoirradiation by UV light. For example, it is known that photoirradiation of retinyl palmitate (RP) by UVA light generates reactive oxygen species, induces lipid peroxidation and causes DNA single strand cleavage in supercoiled ΦΧ174 plasmid DNA. Additionally, it has been shown that the phototoxicity of RP in human skin Jurkat T-cells also leads to cytotoxicity and DNA damage.

Top picks

Here we’ll look at some of the most popular retinoids (available on amazon). These are the most popular in terms of customer satisfaction (in no particular order). This is not an exhaustive list, there are sure to be many more well-loved retinoids out there.

The INKEY List Retinol Serum, 1% – 4.6/5

Key ingredients:

• 1% RetiStar stabilised Retinol
• 0.5% Granactive Retinoid
• Squalane

Olay Regenerist Retinol24 Night Face Cream – 4.5/5

Key ingredients:

• Retinyl Propionate
• Retinol
• Palmitoyl Pentapeptide-4
• Niacinamide

CeraVe Skin Renewing Retinol Serum – 4.4/5

Key ingredients:

• Encapsulated retinol
• Ceramides
• Hyaluronic Acid
• Niacinamide

No7 Advanced Retinol 1.5% Complex Night Concentrate Skin Transforming Accelerator – 4.4/5

Key ingredients:

• 0.3% Pure Retinol
• Matrixyl 3000+ – No7’s anti-wrinkle peptide technology
• Bisabolol – the active component in chamomile helps to minimise irritation by calming and soothing the skin
• Palmitoyl tripeptide-1
• Palmitoyl tetrapeptide-7

The Ordinary Retinol 0.5% in Squalane – 4.6/5

Key ingredients:

• Retinol
• Squalane

Peter Thomas Roth Retinol Fusion PM Night Serum – 4.4/5

Key ingredients:

• Encapsulated retinol
• Squalane
• Vitamin C
• Vitamin E

Neutrogena Rapid Wrinkle Repair – 4.4/5

Key ingredients:

• Retinol SA
• Glucose Complex
• Hyaluronic acid

References

Repa JJ, Hanson KK, Clagett-Dame M. All-trans-retinol is a ligand for the retinoic acid receptors. Proc Natl Acad Sci U S A. 1993;90(15):7293-7297. doi:10.1073/pnas.90.15.7293

Sorg O, Antille C, Kaya G, Saurat JH. Retinoids in cosmeceuticals. Dermatol Ther. 2006;19(5):289-296. doi:10.1111/j.1529-8019.2006.00086.x

Zasada M, Budzisz E. Retinoids: active molecules influencing skin structure formation in cosmetic and dermatological treatments. Postepy Dermatol Alergol. 2019;36(4):392-397. doi:10.5114/ada.2019.87443

Szymański Ł, Skopek R, Palusińska M, et al. Retinoic Acid and Its Derivatives in Skin. Cells. 2020;9(12):2660. Published 2020 Dec 11. doi:10.3390/cells9122660

George Zhu. Vitamin A and its Derivatives- Retinoic Acid and Retinoid Pharmacology. Am J Biomed Sci & Res. 2019 – 3(2). AJBSR.MS.ID.000656. DOI: 10.34297/AJBSR.2019.03.000656

Antille C, Tran C, Sorg O, et al. Vitamin A exerts a photo-protective action in skin by absorbing UVB radiations. JInvest Dermatol 2003: 121: 1163–1167.

Tolleson WH, Cherng SH, Xia Q, et al. Photodecomposition and phototoxicity of natural retinoids. Int J Environ Res Public Health. 2005;2(1):147-155. doi:10.3390/ijerph2005010147