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In my consideration of various retinol products, I investigated the ingredients in Green Cream, which gets good marks from many of this board's members. As far as I can tell, almost all the ingredients are non-irritating, or non-comedogenic. However, the cream's second ingredient – which means it's present in high amounts – is ethanol. I find it troubling that an alcohol would be such a major ingredient (even before the retinol) in this product, especially since info on the Greem Cream Web site cautions against using tonors/astringents because they contain alcohols, which dry the skin.

Or am I mistaken? Is ethanol really one of the "benign" alcohols?

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Lion Queen.....where are you you???

I've been doing a little side research as to weather or not topically applied retinol is actually converted into retinoic acid in epidermal cells. There is a presence of enzymes required for the oxidation of retinol into retinoic acid but they are not very active and in low concentrations in epidermal cells. So it seems that differentiating epidermal cells can make this conversion, but it only happens effectienly at pH of 8.5-9.0, and the pH of skin is 4.2-5.6.....this is why the conversion works in vitro.....but not in vivo....It's interesting that the Green Cream is carbomer based....carbomer requires neutrelization by a base to make it able to gel water. I believe (not looking at the ingredient listing) that it is TEA or triethanolamine....so the pH of the product must be at least 7.5, but probably higher.......

Also the conversion only occurs in differentiated keratinocytes, and not in non-differentiated ones........and also the results of this study confirm that retinal (retinyl aldehyde) is a better starting point than retinol for the conversion into retinoic acid.......

This study was super helpful....and I have the full text.....very informative....... here's an abstract....

Retinol and retinal metabolism. Relationship to the state of differentiation of cultured human keratinocytes.

G Siegenthaler, J H Saurat, and M Ponec

Clinique de Dermatologie, Hôpital Cantonal Universitaire, Geneva, Switzerland.

Abstract

Cultured keratinocytes offer an attractive model for studying the metabolism of retinol in relation to cell differentiation, since the extent of keratinocyte differentiation can be modulated experimentally. The metabolism of retinol and retinal was studied in cytosol fractions prepared from two distinct keratinocyte populations, differentiating and non-differentiated. The enzymic activities were analysed using physiological concentrations of [3H]retinol and [3H]retinal in the presence of cofactors. The products formed were quantified by h.p.l.c. In the population of differentiating keratinocytes, the formation of retinoic acid from retinol occurred at a rate of 4.49 +/- 0.17 pmol/h per mg of protein, but no such conversion was observed in the population of non-differentiated cells. However, when retinal was used as substrate, retinoic acid was formed in both cell populations, at rates of 14.4 pmol/h per mg of protein in non-differentiated and 51.6 pmol/h per mg of protein in differentiating keratinocytes. Using PAGE/radiobinding assay, we demonstrated that retinoic acid formed from retinol was bound in differentiating keratinocytes to endogenous cellular retinoic acid-binding protein (CRABP). Furthermore, retinal was reduced to retinol in the presence of NADH in both differentiating and non-differentiated keratinocytes at a similar rate (8 pmol/h per mg of protein). Although retinal could not be detected under physiological conditions, it was found in significant amounts at pH 8.5-9, which is optimal for enzymic activity. This indicates that in keratinocytes retinal is an intermediate metabolite in retinoic acid formation from retinol. The enzymes catalysing the conversion of retinol into retinoic acid were found to differ from other alcohol and aldehyde dehydrogenases, since the formation of retinoic acid was not significantly affected by specific inhibitors of alcohol metabolism, such as 4-methylpyrazole and disulfiram. Moreover, the cytosol of non-differentiated keratinocytes did not generate retinoic acid from retinol despite showing alcohol dehydrogenase activity. The results suggest that: (1) retinol metabolism in human keratinocytes is different from that of other alcohols, (2) retinal is an intermediate metabolite in the conversion of retinol into retinoic acid, and (3) differentiating keratinocytes rich in CRABP are probably target cells for retinoic acid action.

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