Thin Jim said:
Guys I have never found an answer to this question. Has it been determined the actual Radius that minoxidil absorbs under the scalp.
As far as I know, that has never been directly tested by doctors or scientists, except to the very limited extent described in the study below. All we really have are just anecdotes and speculation, although it does seem fairly clear that the effect of topical minoxidil extends at least to some degree outside of the actual physical area to which it's applied.
But here's an interesting study with a "twist" to it that's fairly relevant to this question: "Double-blind, placebo-controlled evaluation of topical minoxidil in extensive alopecia areata", Vera H. Price, J Am Acad Dermatol 1987; 16:730-6. Here's the "twist", as described in the treatment protocol section (added emphasis in
bold is my own): "Subjects were randomly assigned in a double-blind fashion to receive either the 3% minoxidil solution or placebo. The assigned solution was applied twice daily to affected areas
on half of the scalp only, with overnight petrolatum occlusion. The other half of the scalp was left untreated throughout the 1-year study."
The treatment was generally successful, and here's what Price says in the Discussion section: "Subjects in the minoxidil group who regrew scalp hair had growth on both the treated and untreated sides, but hair growth always began earlier and was more abundant on the treated side. Hair growth on the untreated side of the scalp in the minoxidil group may have been either spontaneous regrowth or a response to the minoxidil in the nearby scalp areas.
There is some speculation that topical minoxidil spreads across the skin surface or even within the skin, much like solvents through chromatograph paper. Alternatively, topical minoxidil may be transferred from the treated side to the untreated side by wigs, hats, or pillowcases. A systemic effect is unlikely in view of the low to very low minoxidil serum levels measured."
So that supports the general idea that topical minoxidil does work mainly on the parts of the scalp where it's directly applied, but the effect _may_ indeed spread-out a little to neighboring areas. I think you should always try to apply it directly to all the affected areas that need it, but even if you miss a spot here or there, you'll still probably get some noticeable effect in the places you missed.
