The Transdermal Absorption of Retinol and Retinyl Palmitate in Cosmetics Formulations
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Presented by: Yuan-Po Lee
Since The Cosmetic Ingredient Review (CIR) Expert Panel concludes that retinol and retinyl palmitate are safe as cosmetic ingredients in the present practices of use and concentration in 1987. There are numerous studies concerning about the safety and stability of retinol and retinyl palmitate thereafter. Retinol and retinyl palmitate are commonly used in topical antiaging preparations. Excessive intakes of vitamin A has been linked to increased risk for hypervitaminose A and whether frequent application of skin care products containing retinol or retinyl esters could result in long term effects in skin. Therefore, a clear understanding about the transdermal absorption of retinol and retinyl palmitate is essential for the safety evaluation of these ingredients in cosmetics.
In this study, the effect of formulation, type and concentration of enhancers on the transdermal absorption of retinol and retinyl palmitate have been investigated. Three types of formulation, including essence, w/o and o/w emulsions, were prepared for this study. Propylene glycol, 1,3-Butylene glycol or glycerin in the concentration of 5% or 10% were used to study the transdermal absorption enhancement effect for essence. The transdermal absorption test procedure is refer to the OECD Test Guideline 428 - Skin Absorption: In Vitro Method.
The transdermal absorption test was performed by apply 0.01g sample (essence, w/o or o/w emulsions) on excised pig skin with exposed area of 0.64cm2 at 37oC for 10 hours with 6 duplicates. The data is accepted only when it reaches mass balance, which is the mass difference of test chemical applied to the system and the overall chemical collected after test is smaller than 15%。The mass of test chemical after test was collected from the amount in flush collected residue sample, the amount on cotton buds for dry the skin, the amount on stripping tape, the amount diffused into the skin and the amount delivered across the skin collected in receptor determined by HPLC.
The results show that retinol has stronger transfer ability to diffuse into and delivered across of the dermal layer than retinyl palmitate, this should be due the molecular size difference. Higher molecular weight of retinyl palmitate is harder to move cross the stratum corneum, which is demonstrated by the determined amount on stripping tape, which is around 3-6% for retinol and around 11-20% for retinyl palmitate for all the tests.
Without enhancer, the transdermal absorption amount, the amount diffused into the skin and the amount delivered across the skin, of retinyl palmitate is around two third of that of retinol. With 5% propylene glycol as enhancer in essence, the transdermal absorption amount of retinol and retinyl palmitate are both increased to around 20% and retinyl palmitate is all stayed at the dermal layer.
For comparing the effect of formulation type on the transdermal absorption, the transdermal absorption amount of retinol is almost the same for essence and o/w emulsion, however the transdermal absorption amount of retinyl palmitate is slightly lower in o/w emulsion than in essence. Nevertheless, the transdermal absorption amount of retinol and retinyl palmitate in w/o emulsion is the lowest among the three formulation types.
About the effect of enhancer type and concentration on the transdermal absorption, it was studied only for essence. Generally, essence with enhancer, propylene glycol gives better transdermal absorption result than 1,3-Butylene glycol and then glycerin. 5% propylene glycol, 1,3-Butylene glycol or glycerin also shows better transdermal absorption result than 10% propylene glycol, 1,3-Butylene glycol or glycerin. It was also noticed that retinyl palmitate is all retained on the dermal layer without transfer across it. Furthermore, 5% propylene glycol and 5% glycerin are giving higher amount delivered across the dermal layer.
In conclusion, the retained amount in dermal layer of retinyl palmitate from essence and o/w emulsion are higher than retinol. For cosmetics, use retinyl palmitate as active gradient with enhancer may be able to decrease the active gradient concentration in the formulation and still achieve the effective concentration with less safety concern.
In this study, the effect of formulation, type and concentration of enhancers on the transdermal absorption of retinol and retinyl palmitate have been investigated. Three types of formulation, including essence, w/o and o/w emulsions, were prepared for this study. Propylene glycol, 1,3-Butylene glycol or glycerin in the concentration of 5% or 10% were used to study the transdermal absorption enhancement effect for essence. The transdermal absorption test procedure is refer to the OECD Test Guideline 428 - Skin Absorption: In Vitro Method.
The transdermal absorption test was performed by apply 0.01g sample (essence, w/o or o/w emulsions) on excised pig skin with exposed area of 0.64cm2 at 37oC for 10 hours with 6 duplicates. The data is accepted only when it reaches mass balance, which is the mass difference of test chemical applied to the system and the overall chemical collected after test is smaller than 15%。The mass of test chemical after test was collected from the amount in flush collected residue sample, the amount on cotton buds for dry the skin, the amount on stripping tape, the amount diffused into the skin and the amount delivered across the skin collected in receptor determined by HPLC.
The results show that retinol has stronger transfer ability to diffuse into and delivered across of the dermal layer than retinyl palmitate, this should be due the molecular size difference. Higher molecular weight of retinyl palmitate is harder to move cross the stratum corneum, which is demonstrated by the determined amount on stripping tape, which is around 3-6% for retinol and around 11-20% for retinyl palmitate for all the tests.
Without enhancer, the transdermal absorption amount, the amount diffused into the skin and the amount delivered across the skin, of retinyl palmitate is around two third of that of retinol. With 5% propylene glycol as enhancer in essence, the transdermal absorption amount of retinol and retinyl palmitate are both increased to around 20% and retinyl palmitate is all stayed at the dermal layer.
For comparing the effect of formulation type on the transdermal absorption, the transdermal absorption amount of retinol is almost the same for essence and o/w emulsion, however the transdermal absorption amount of retinyl palmitate is slightly lower in o/w emulsion than in essence. Nevertheless, the transdermal absorption amount of retinol and retinyl palmitate in w/o emulsion is the lowest among the three formulation types.
About the effect of enhancer type and concentration on the transdermal absorption, it was studied only for essence. Generally, essence with enhancer, propylene glycol gives better transdermal absorption result than 1,3-Butylene glycol and then glycerin. 5% propylene glycol, 1,3-Butylene glycol or glycerin also shows better transdermal absorption result than 10% propylene glycol, 1,3-Butylene glycol or glycerin. It was also noticed that retinyl palmitate is all retained on the dermal layer without transfer across it. Furthermore, 5% propylene glycol and 5% glycerin are giving higher amount delivered across the dermal layer.
In conclusion, the retained amount in dermal layer of retinyl palmitate from essence and o/w emulsion are higher than retinol. For cosmetics, use retinyl palmitate as active gradient with enhancer may be able to decrease the active gradient concentration in the formulation and still achieve the effective concentration with less safety concern.