Members Section

A primary function of skin is to serve as a barrier against penetration by exogenous molecules in the daily environment of man. Damaged, aged and skin thinned due to other causes more readily allows the penetration of all kinds of molecules at relatively low concentration. Lipophyllic substances always penetrate the skin more readily than hydrophyllic ones. The quality of inter-cellular connections, lipids and proteins determine the efficacy of the skin barrier.

Vitamin A is the essential factor involved in differentiation of new skin cells and the production of high quality protein and lipids in the skin. It increases the efficacy with which the different cellular and fibrous elements bind to each other, increasing the barrier function and tensile strength of the skin by improving the laminate structure.

As the positive effects of vitamin A accumulate over time the barrier function of the skin is progressively enhanced. Consequently it becomes more difficult to get any molecule, including vitamin A, to penetrate the skin.

This phenomenon can be described as the 'Vitamin A paradox' and clearly explains the need for increasing the dosage of topical vitamin A over time. The paradox also illustrates the need for advanced penetration techniques like application of toners, iontophoresis, sonophoresis and punching temporary holes through the epidermis by specialized epidermal needling.

Individual skin requirements for vitamin A differ according to vitamin A receptor characteristics of a person’s skin, but the principle of increased vitamin A dosages over time is universally applicable.

References

• [1].Introduction, Braham Shroot, Retinoids A Clinician's Guide, Second Edition, page 1, Edited by Nicholas J Lowe and Ronald Marks , Publisher Martin Dunitz 1998.
• [2.] Vitamin A and Caretenoids: Flexible Actions of Inflexible Molecules, James Allen Olson, Retinoids: From Basic Science to Clinical Applications, Edited by M A Livrea and G Vidali, Page 11 - 19 Published by Birkhauser 1994.
• [3] F Chytil New Horizons in Retinoid Research, Retinoids: From Basic Science to Clinical Applications, Edited by M A Livrea and G Vidali, Published by Birkhauser 1994.
• [4] Modulation of retinoid metabolism by binding proteins. David E Ong et al. Retinoids: From Basic Science to Clinical Applications, Edited by M A Livrea and G Vidali , page 79-89 Published by Birkhauser 1994.
• [5] Retinoid nuclear receptors. Roshantha AS Chandraratna, Elliott S Klein Retinoids A Clinician's Guide, Second Edition, page 22-32, Edited by Nicholas J Lowe and Ronald Marks, Publisher Martin Dunitz 1998.
• [6] Retinoid Response Pathways Magnus Pfahl, Retinoids: From Basic Science to Clinical Applications, Edited by M A Livrea and G Vidali, page 115-126 Published by Birkhauser 1994.
• [7] Ultra-violet Irradiation of human skin causes functional vitamin A deficiency, preventable by all-trans retinoic acid pre-treatment. Wang et al., Nature Medicine 1999, 5, 418 - 422.
• [8] Blomhoff R. Vitamin A in Health and Disease, Marcel Dekker, New York 1994.
• [9] Receptors, Models for Binding, Trafficking and Signalling, Douglas Lauffenburger, Jennifer Linderman, Oxford University Press 1993.
• [10] Rusting of the Epidermal Engine, R Marks, Retinoids 1999, Vol. 15 No3, Page 86-88.
• [11] Ligand Induced Transcription By Nuclear Receptors, D M Heery, M G Parker, Retinoids 1997, Vol. 13 No 1, Page 26 – 30.
• [12] Retinoid Receptors, H Törmä, Retinoids 1997, Vol. 15 No 3, Page 101.