Introduction

“Vitamin A is the first vitamin approved by the Food and Drug Administration as an anti-wrinkle agent that changes appearance of the skin surface and has anti-aging effects.”^​1​

Retinol (Vitamin A) and the retinoids are a family of naturally occurring and widely used cosmetic skincare ingredients. There are a number of compounds in this family with the active compound being trans-retinoic acid (trans-RA)^​2​. All other retinoids forms are ultimately converted in the skin to trans-RA to deliver the skincare benefits^​3​. Retinoids are an extensively researched group of skincare ingredients and the skin benefits are well established^​4​. However, there are two considerable challenges in formulating with retinoids; they can be highly skin irritating and they can be highly unstable in formulation^​2​.

Benefits for Your Skin

“Vitamin A (Retinol) and its derivatives are among the most effective substances slowing the aging process.”^​1​

Retinoids are well known as anti-aging compounds and various members of this group offer the following clinically proven skin benefits^​1,3,5​:

• Increase epidermal skin turnover to produce more youthful skin
• Increase collagen and elastin synthesis to reduce wrinkles and fine lines
• Improve skin texture
• Inhibit melanin production to reduce skin pigmentations
• Improve skin firmness, hydration and elasticity
• Treat incidence of acne and inflammations
• Treat photoaged skin

Challenges to Retinoid Cosmetic Use

“The irritant effect of vitamin A and its derivatives and their instability are factors limiting their use in cosmetic and pharmaceutical products.”^​1​

Retinoids and skin Irritation

Whilst retinoids hold out many proven anti-aging skincare benefits, their tendency to irritate the skin often prevents realisation of those benefits^​1​. Trans-RA, the skin-active retinoid, is highly skin irritating in even low doses and can only be professionally prescribed in most countries. Most over the counter retinoid skincare products use either retinol of retinol esters such as retinyl palmitate. These are less active that trans-RA, still deliver similar antiaging and anti-acne results but are far less skin irritating. Both retinol and retinyl palmitate are converted in the skin to trans-RA.

Retinyl palmitate has very low irritation potential and, while it is less efficacious than retinol, it can be formulated at higher concentrations to increase effectiveness^​2​. Retinyl palmitate is also the primary skin storage form of retinol and so is much less skin irritating than other retinoid forms.

“In order to minimize these side effects, various novel drug delivery systems have been developed. In particular, nanoparticles have shown a good potential in improving the stability, tolerability and efficacy of retinoids.”^​6​

Retinoid Stability

Retinol is extremely unstable, especially in the presence of light and oxygen^​2,6​. Although many cosmetic formulations use retinol, it is considered too unstable^​2​ for water based cosmetic formulations and quickly breaks down in presence of air and light^​7​. Retinyl palmitate is more stable than retinol and is a better ingredient for cosmetic formulations.

“The vehicle used for retinol delivery would play a crucial role in eliciting its efficacy, as retinol is extremely unstable and easily gets degraded to biologically inactive forms on exposure to light and air.”^​6​

Retinoids and Microemulsion Delivery

In recent years, microemulsion formulations have been used to improve the stability and effectiveness of retinoid treatments. A nano-based formulation system using retinyl palmitate demonstrated enhanced safety and higher antioxidant activity in topical application of retinyl palmitate.^​8​

In another study, low-energy, nano-encapsulation of retinyl palmitate provided increased retinyl palmitate UV and storage stability, superior solubilisation and enhanced skin permeation^​9​. The increased skin permeation efficiency of microemulsions offer the possibility of formulations with lower concentrations of irritating actives to achieve the same effectiveness.

“Employment of the nano-encapsulation approach afterward dispersion into hydrogel system for the development of a topical delivery system of retinyl palmitate resulted in improvement in its UV and storage stability as well.”^​9​

Discussion

Retinol and retinoids offer considerable antiaging, anti-inflammatory and acne treatment benefits for the skin. However, the effectiveness of cosmetic topical retinol applications have been hampered by the twin challenges of skin irritability and formulation instability. Retinol is too unstable for inclusion in topical cosmetic formulations. Retinyl palmitate, a natural skin storage form of retinol, while being less effective than retinol is less irritating and much more stable in formulation.

The use of new generation cosmetic formulation microemulsion systems such as our Green Micelle™ formulation system overcome these stability problems and offer a stable formulation with enhanced solubility and skin penetration ability.

References