vitamins can be utilised via topical administration - B6 pyridoxine is converted to B6 pyridoxal both internally and via skin mechanism.
B6 potentialises a 5aR inhibition effect of zinc according to the following study...
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Br J Dermatol 1988 Nov;119(5):627-632
Inhibition of 5 alpha-reductase activity in human skin by zinc and azelaic
acid.
When added at concentrations of 3 or 9 mmol/l, zinc was a potent
inhibitor of 5 alpha-reductase activity. At high concentrations, zinc
could completely inhibit the enzyme activity...
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Another study shows zincs ability to reduce 5aR type I...
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Cations inhibit specifically type I 5 alpha-reductase found in human skin.
Author: Sugimoto Y; López-Solache I; Labrie F; Luu-The V
Medical Research Council Group in Molecular Endocrinology,
CHUL Research Center, Quebec, Canada.
Source: J Invest Dermatol, 104: 5, 1995 May, 775-8
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I don't know whether it works, but I'm currently tring it in a 50/50 aloe & water mix with 10% MSM - if nothing else I'm getting scary as hell hair growth - around an inch per month