Retinoid is a term used to classify Vitamin A compounds. It turns out that there are many different types of Vitamin A, so the general term retinoid covers a lot of them. Vitamin A is found naturally in the skin and other parts of the body and is obtained through the diet while eating foods like sweet potatoes, carrots, dark green leafy vegetables, tomatoes, squash, and tropical fruits. Retinoids have long been used topically to help repair sun-damaged skin and reduce fine lines and wrinkles. In addition, it is thought these materials can smooth skin, unclog pores, address hyper-pigmentation and improve skin texture.
Types of retinoids
The various retinoids found in skin care include natural versions such as tretinoin, isotretinoin, alitretinoin, retinol, and retinaldehyde. There are also the synthetic versions including tazarotene, adapalene, and retinyl palmitate or other retinyl esters. Retinol and retinyl esters represent 99 percent of cutaneous retinoids naturally present in the skin. While many of the retinoids occur naturally, the ingredients that are put into formulas are synthetically produced in a lab.
How a retinoid is formulated can also affect how effective it is. For example, alcohol-based gels are considered the most effective formulations because they more easily absorb into the skin. They’re often used for oily or acne-prone skin. Remember these ingredients depend on penetration to get them to work most effectively.
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How retinoids might work
Retinoic acid is thought to fade dark spots by reducing the contact time between skin surface cells and the pigment creating cells. It reduces fine lines/wrinkles by stimulating synthesis of collagen and glycosaminoglycan. Also, it may inhibit enzymes that breakdown collagen. Finally, it can smooth out the skin by modulating the genes involved in epidermal cell turn over.
Can it penetrate skin to get to where it needs to be in order to work? Yes. Retinol has the right chemical structure to penetrate skin and this has been confirmed two ways: In vivo by measuring the level of a skin enzyme induced by presence of retinoic acid. (Also confirms metabolism to active version.) In vitro by measuring retinol metabolites on skin biopsies and cell cultures. There are some unresolved questions about how much bio-converts, however.
Effectiveness of retinoids
Tazarotene. This is said to be the most powerful retinoid available, but it is only something you can get by prescription, at least in the US.
Tretinoin, also known as retinoic acid. This is another potent retinoid available by prescription only. It has been proven clinically effective for the treatment of photoaging.
Adapalene. This retinoid is now available in over-the-counter products. This may be one of the most effective retinoids for which a prescription is not required. It’s also the first FDA-approved OTC retinoid for acne.
Retinol. This is the standard ingredient found in OTC retinoid products. Although it is widely believed to be effective, it has not undergone the process to get it approved as a drug in the same way as tretinoin and tazarotene have. For retinol to work it needs to be converted in the skin to the acid form. This process is not completely efficient, so it is unsurprising that retinol is less effective than retinoic acid. However, it is also less irritating which can be important to consumers.
Retinyl Retinoate is another type of synthetic retinoid ester. In a couple of studies, it was shown to be superior in performance to Retinol, so this is one that may be used more often in the future. One main reason is because it is easier to stabilize than retinol.
Retinaldehyde, which exhibits slightly more efficacy than retinyl esters, is generally well tolerated, and appears to renew epidermal cells, blunt the effects of photoaging, and limit oxidative stress and bacterial flora on the skin. If a consumer has sensitive or delicate skin, but still wants the effects of retinoids without a prescription, this may be a good option.
Retinyl palmitate. While this ingredient is a natural storage form of retinoids in the skin, it is also found to be less effective than other retinoids. It also has the problem of potentially being a photosensitizer, but it is also one of the ones that is least likely to cause irritation, so you find it in a lot of products.
Topical application
The studies on Vitamin A derivatives are promising, but as with many of these cosmeceuticals, there have been few large-scale double-blinded placebo-controlled trials looking at the clinical benefits of any of the OTC Vitamin A derivatives.
But Retinoic Acid has undergone extensive clinical testing as have the retinoids that require a prescription. Fewer studies have been done on the over-the-counter versions. Retinol was shown to be effective vs placebo, but not as effective when compared to retinaldehyde for wrinkle reduction.
The mechanism and effects of retinoic acid are well understood, and it appears that other retinoids work the same way just to a lesser extent, however the OTC versions are not as well substantiated as the prescription form.
The drawbacks to retinoids include; they are unstable, difficult to formulate with, can cause irritation, many products that claim to have retinoids don’t actually work because they aren’t properly stabilized, and it’s suggested that they only be used at night due to potential reactions with UV.
Because of these problems, people are continually on the lookout for other options. One extract that is often talked about in relation to retinoids is Bakuchiol extract because it appears to have the same effectiveness without the drawbacks. We’ll save that topic for another day.
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