Retinoids includes vitamin A and compounds similar to vitamin A. Vitamin A is a group of compounds which are essential for many functions in the body. Depending on age, sex, and pregnancy human need somewhere between 0.35 and 1.1 g of vitamin A per day. The focus here will be on Retinoids and the skin.
Retinoids is a large group of biologically active substances which primarily perform their effect by influencing the genome. This impact takes place by means of specific retinoid receptors, of which there are two types: Retinoic Acid Receptors (RAR) and Retinoid X Receptors (RXR).
At the cellular level, Retinoids can stimulate cellular activity in a variety of skin cells such as keratinocytes, fibroblasts, melanocytes and Langerhans cells. This can result in positive effects such as increasing the protective function of the epidermis, reducing water loss (and thus dry skin), protecting collagen from degradation, and inhibiting the activity of certain enzymes responsible for the degradation of the extracellular matrix. In addition, some (primarily in vitro and animal experiments) studies have shown that some Retinoids have an antioxidant and anti-bacterial effect.
Many Retinoids are researched and have shown positive effects in relation to e. g. wrinkles, pigment spots and impure skin – and some side effects such as skin irritation and possible endocrine disrupting effect. As with everything else, it is about finding the right balance.
There are both natural and synthetic retinoids and they are often divided into three generations of retinoids based on their molecular structures.
Retinoids are usually fat-soluble compounds with a ring-shaped structure, on which there is a chain with alternating double and single bonds between the C atoms. At the end of the chain is the structure that most often makes the difference between the most well-known Retinoids.
Alone, Retinoids are often not very stable, which is why they are often stabilized in relatively complex raw materials by the raw material producer – where the retinoid content itself is typically between 1 and 10%. Thus, a cosmetic product can contain, for example, 5% of a retinoid raw material, and if this retinoid raw material contains 1 % Retinoid then the proportion of “pure” Retinoid in the finished product is 0.05%. It is different how manufacturers state the amount of retinoid – some state the proportion of the raw material (including solvents, stabilizers, and retinoid) and others state the proportion of “pure” Retinoid. In some cases, the raw material is also formulated in a special way, which can help for better skin penetration and / or a slower release and thus less risk of unwanted side effects.
It is often recommended to avoid the sun or to use sunscreen in conjunction with retinoid use – primarily because retinoids can be unstable in sunlight. However, there are also studies which show that some retinoids have a UV-filter effect as they absorb UV light.
Below, the most common Retinoids are reviewed.