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Since the discovery of retinol and other retinoid skin benefits in the 80’s, they have been consistently added to cosmetic products to enhance skin vitality. However, research in decades since has challenged their effectiveness in cosmetic products due to their highly reactive nature.
The following discussion takes a look at retinoids in cosmetics, evaluating which one (if any) would be most beneficial in an everyday skincare routine. Retinoid benefits, side effects, metabolism and specific types are detailed below.
What are Retinoids?
A retinoid is the official term for any derivative of retinol, more commonly referred to as Vitamin A. Vitamin A is not just one compound, but rather refers to a class of Vitamin A compounds which are the same or similar in structure and biological function. The body and many living organisms contain vitamin A receptors and utilize vitamin A and it’s derivatives in several vital biological processes pertaining to cellular growth, immune stability, nerve function and eyesight.
The membranes of skin cells require vitamin A (amongst other nutrients) in order to regenerate, grow, regulate pigmentation and remain strong in the face of UV damage. In the beauty arena, retinol and retinoids are revered for the way they maintain the health of aged and damaged skin.
Types of Vitamin A
Vitamin A compounds are classified according to whether they are natural or synthetic. Natural retinoids are considered to be first generation retinoids and are found everywhere in nature, including inside our cells. Since the discovery of retinol and it’s natural derivatives, over 5000 retinoids have been synthesized, leading to 2nd, 3rd and 4th generation derivatives.
Each generation of retinoids lends itself to further synthetic alterations that take them further away from natural Vitamin A counterparts. For instance, second generation retinoids mimic first generation retinoids, with the only difference being the outer ring replacement of cyclohexane with synthetic benzene. Third generation retinoids are altered synthetic retinoids that are designed with specific retinoid receptor interactions in mind, usually only used in treating skin conditions.
How Retinoids Work in Skin
Retinol and some retinoids can be used by skin cells immediately, while others require a bit of processing beforehand. In order for the cell to use a retinoid, it has to activate the right receptor. Just about all tissues in the body have retinoid receptors. Under natural circumstances, these are activated by the biologically active form of retinol, known as retinoic acid. Retinoic acids are again referring to a group of compounds that activate receptors in various ways, leading to results that help the cell maintain and regulate its inherent function.
Retinol is animal-based vitamin A and is found throughout all animal tissues alongside its storage form, retinoid esters. Retinoid esters can be oxidized into retinol as required and do not activate retinoid receptors. In spite of this, they also have biological actions when merely being stored in skin tissue, able to absorb UVB radiation and protect the skin. Evidence suggests that stores of retinoids in the body are used up when one is not consuming or absorbing enough vitamin A and that maintaining Vitamin A stores is vital to overall health and skin vitality .
When retinol is metabolized by skin cells, it is converted via enzymes into retinal (aka retinaldehyde) and is then further converted into retinoic acid and its active metabolites before exerting an effect. Plant-based forms of vitamin A can be oxidized to produce retinal or retinol and include carotenoids such as beta-carotene.
All of these retinoids have been added to cosmetic products, with differing potencies and similar benefits.
Benefits of Cosmetic Retinoids
Retinoids in skin have a number of benefits, including:
- Promoting collagen synthesis and preventing collagen degradation
- Reducing wrinkle count
- Enhancing skin water retention
- Protecting against UV radiation-induced skin damage
- Reducing sebum (skin oil) production
- Lowering the chance that pores will get blocked (anti-comedogenic effects)
- Beneficially modulating immune function
- Serving as an antioxidant under the right conditions
- Regulating melanin deposition in the skin
As a result, retinoids have been used in cosmetic products to reduce the incidence of acne, lighten the skin, improve the quality of aged skin, help protect against sunburn and photodamage, as well as to treat many inflammatory skin diseases.
The benefits of retinoids are often accumulative over time, taking 2-3 months to produce results.
How Effective Are Topical Retinoids?
In spite of the documented benefits, not all topical application of retinoids work effectively to counter sun damage. The form used, the concentration, how it is stored, other ingredients it may be paired with and the delivery method all impact how effective a retinoid is when topically applied.
One problem with retinoids is that they are highly unstable, quickly able to oxidize at temperatures above 2˚C or in sunlight, which makes them less effective and sometimes even harmful to skin. To lower unintended side effects, the addition of other antioxidants in skin formulations, like ascorbic acid, may help to slow down retinoid oxidation. A high water content in cosmetic products may detract from the stability of vitamin A, as might exposure to direct sunlight and heat. This in turn will increase side effects experienced, as will larger concentrations of the vitamin. Compounds that are able to keep retinoids bound, such as clay, may help in this respect but may detract from skin penetration.
Dermatologists that prescribe retinoids recommend only applying them at night time to minimize degradation by sunlight. Refrigerating retinoid-containing products can also be of great use in this regard.
Another issue is delivery, as these fat-soluble compounds don’t tend to penetrate very deeply into the skin, only really impacting the surface layers. In this respect, they may not help to reduce the appearance of deep set wrinkles. Pharmaceutical preparations have been developed that allow for retinoids to reach deeper layers of the skin.
Which is the Best Retinoid for Use in Cosmetics?
Synthetic retinoids tend to be too potent for everyday cosmetic use and are usually only prescribed by skincare specialists for niche applications, such as psoriasis or severe acne. Natural retinoids are discussed below in terms of their effectiveness in an everyday skincare routine.
Retinol and Retinal
Out of all the retinoids tested, the natural retinoids retinol and retinal were the best for cosmetic use. They penetrated the skin deeper, with all data revealing that they are capable of penetrating the stratum corneum (superficial layer of dead skin cells, oil, etc) into the epidermis (top skin layer). Some studies suggest that retinol can penetrate to the base layers of the epidermis, while others indicate that it can penetrate even deeper into the dermis, exerting beneficial effect there as well.
Furthermore, retinol and retinal increased all forms of vitamin A in the skin, including retinol, retinal, stored retinol esters and highly active retinoic acids. By contrast, applying retinoic acid and other forms directly to skin did not penetrate deep enough to make much difference, unless specially prepared for pharmaceutical use. Furthermore, retinal and retinol were better tolerated by skin on average, with retinal having a more potent action than retinol.
Retinal is also the only retinoid with antimicrobial effects, however these effects are due in part to it’s highly volatile nature. In this respect, retinol is likely to be better tolerated when directly applied to skin.
Retinoic acids are the strongest Vitamin A forms with the highest biologic activity. There are different types of retinoic acid, with tretinoin being the most potent of the lot. Tretinoin has a biologic action that is 20 times stronger than retinol. Unfortunately it does not penetrate the skin deep enough to exert much benefit without specialized formulation and is equally capable of exerting side effects that are 20 times as potent as retinol.
For those with severe skin conditions, special tretinoin formulations have been devised that help treat the skin. It should be noted that the concentration of tretinoin is very small in these formulations (0.05-0.3%) and that retinol still has better tolerability on average.
Retinol Ester Derivatives
Retinol ester derivatives including, retinyl palmitate and retinyl acetate, are associated with generating inflammation in the skin and are being investigated as potential carcinogens.
In those who can tolerate it, studies reveal that applying ester derivatives topically does in fact increase the stored forms of Vitamin A in the skin, however it does little else. Comparatively, retinol and retinal still did a better job, allowing for the skin to dictate how the vitamin A ought to be utilized.
When retinoic acid oxidizes, it produces oxo-retinoids as by-products. These were previously thought to be inactive, however animal studies have shown them to induce inflammation, hyperactive skin growth, and skin immune suppression. Furthermore, the skin does not transform them back into retinoic acid or another bioavailable form. These forms of Vitamin A are essentially a waste product and may occur in cosmetic products containing retinoids.
Retinoid Side Effects
In spite of their benefits, nearly all retinoids come with side effects when used topically. Side effects include:
The majority of topically applied retinoids appear to activate pain receptors in the skin, which irritates the skin in a dose-dependent manner. This applies throughout the body, not only to topically applied retinoids but to orally ingested ones as well.
It would seem that dietary retinoids beta-carotene and retinol palmitate present in animal or plant-based foods do not cause the same irritation. The reason being that the above retinoids directly activate a specific retinoid receptor that goes on to activate pain receptors as a consequence. Digested retinoids are not applied in the same manner and are generally absorbed and distributed throughout the body when supplies require replenishing.
- Toxicity and Skin Hyperplasia
Overuse of retinoids can easily result in Vitamin A toxicity, even though it is usually well tolerated at cosmetic concentrations. Studies on animals and human skin cell cultures also demonstrate that overdoing it with retinoids can lead to excessive growth of the skin; which is not a great sign for those who are at high risk for developing skin cancer.
It follows on from here that Vitamin A can be used with wonderful results if the skin actually requires a boost, such as in the case of aged and photodamaged skin. Those with healthy skin do not require it as much and should perhaps avoid it in their skincare routine, rather focusing on increasing dietary retinoid consumption for increased skin vitality.
The first point to make with regard to retinoid use is that less is more. Topical application of retinoids is best in the elderly, those with rapidly aged and photodamaged skin or those with sunburns. Out of the topical retinoids available on the market, retinol and retinal appear to exert the most benefit with the least side effects.
Retinoid-containing products ought to be kept in the fridge and away from sunlight in order to preserve the active ingredients and lower the risk of skin irritation.
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About the Author:
Mersad Alimoradi is a medical doctor specializing in general surgery, with a big interest in academia. He is passionate about spreading medical knowledge and making it accessible to everyone. He has received his medical degree from the Lebanese University, in Beirut, and currently works as a physician and researcher in the country's university hospitals.
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