When we talk about retinoids in skincare, we are talking about different forms of vitamin A ranging in strength. I want to begin by defining the four types of retinoids we see in skincare:
- Retinoic Acid (RX only): A vitamin A derivative that has demonstrated an ability to alter collagen synthesis and is used to treat acne and visible signs of ageing. Side effects are irritation, photosensitivity, skin dryness, redness, and peeling (Milady Standard Esthetics: Fundamentals (2012), page 749).
Retinoic acid is the bioavailable form, meaning it’s the form that your skin can readily use.
Retinoic acid includes tretinoin (Retin-A), tazarotene (Tazorac), and adapalene (prescription-strength Differin).
- Retinol (Over the Counter): A natural form of vitamin A. It stimulates cell repair and helps to normalize skin cells by generating new cells (Milady Standard Esthetics: Fundamentals, page 749).
This includes anything you can buy without a doctor’s prescription and will be listed as retinol in the ingredients list.
So those two we are familiar with, but there are two other categories of retinoids, the esters. This is where we branch into organic chemistry a little bit, but I am going to try to give you the simplest definition of an ester possible:
An ester is a compound derived from an acid, where hydrogen is replaced by a hydrocarbon.
To simplify this further, esters come from acid, and they are a little different formula-wise. Since the formula is different from the original acid, esters are a weaker form of acid. That is all that is important for us to know. The two forms of vitamin A esters are:
- Retinoic Acid Esters: These will be listed as Retinaldehyde or Granactive (hydroxypinacolone retinoate).
- Retinyl/Retinol Esters: I have seen the spelling both ways. These will be listed as Retinyl Propionate and Retinyl Palmitate
So now that we know the four forms of retinoids, what is the difference between them all?
When applied topically, the skin must convert over the counter forms of retinoids into the bioavailable form (retinoic acid), by chemical conversion.
Depending on the form of retinoid, it may require one, two, or three chemical reactions. Basic chemistry teaches us that when a compound goes through a chemical reaction, the strength of the compound weakens.
So, we must know the form of retinoid we are utilizing to really know the strength. The other important factor to consider is that a weaker retinoid going through chemical conversions can be very irritating to the skin.
Weakest form to strongest form
Retinol Esters -> Retinol -> Retinoic Acid Esters -> Retinoic Acid
We must know this cycle so we can decipher percentages. For example, 1% retinol is weaker than 0.02% retinoic acid due to the chemical conversions it must go through.
Now that we know what to look for with vitamin A, let us look at what happens in the skin. Retinoids claim to increase collagen, lighten hyperpigmentation, and give an overall youthful appearance to the skin, but how is this happening?
Retinoids are considered keratolytic, which means they encourage a quicker turnover of skin cells. This process allows for the sloughing off of skin cells with hyperpigmentation.
Retinoids also have properties that prevent new pigment from forming. In an article titled “Depigmenting mechanisms of all-trans-retinoic acid and retinol on B16 melanoma cells”, Sato et al. (2008) found that the decrease in pigment from the use of retinoic acid and retinol was related to the inhibition of tyrosinase.
Therefore, we see hyperpigmentation decrease significantly over long-term use. Not only are the pigmented corneocytes being sloughed off, but also the pigment chemical reaction is being prevented from taking place.
Retinoids also decrease the appearance of fine lines and wrinkles. In the article titled “A comparative study of the effects of retinol and retinoic acid on histological, molecular, and clinic properties of human skin” by Kong et al. (2016), an increase in epidermal thickness and collagen production was shown in the skin after four weeks of daily use of people who used either retinol or retinoic acid. This indicates that retinoids are stimulating the fibroblasts to produce more collagen and elastin.
In conclusion, retinoids work by exfoliating the corneocytes at an increased pace, increasing collagen production and preventing pigmentation. The type of retinoid selected makes a difference in the amount of these changes in the skin.
Always encourage new retinol users to follow a slow and steady introduction. Remember, retinoids are the tortoise in the race. They will show improvements in the skin, but it requires patience.