Does topical medication (e.g. Rogaine) work when it's dry on the skin?

May 27, 2013 8:54 AM

I've used Rogaine/finasteride and another topical hair-loss treatment. Both say that the product should be applied twice daily, and that more than that won't yield any better results. I'm inclined to trust them - especially since they have an incentive to encourage more frequent use - but intuitively this doesn't seem right. It seems like a topical treatment would really only "work" when it's wet, and that once it's dry it would have much less effect. Am I wrong? Does anyone know the mechanics of how this kind of stuff works?
posted by Mechitar to Health & Fitness (8 answers total)

I don't know how it works at all, but I can tell you I have a friend who's used it, and it did seem to work.
posted by catatethebird at 9:16 AM on May 27, 2013

Well, skin's a lot more permeable than it might seem, plus it has a small amount of oils and whatnot on it all the time. If you stuck your feet in a pile of salt, you would get dehydrated, so I think it is plausible that dry substances would have an effect.

Plus, if the topical treatment needs reapplication, these limitations are likely about the maximum amount of the medicinal ingredient that your body is able to effectively absorb and use at a given time, and the halflife of such ingredients and stuff like that (As a parallel example, imagine you have a peice of leather that needs oiling. There's a limit to how much oil it can absorb, but if you come back a few hours later you can rub in some more. Or if you take vitamins, you pee away a good portion of them and take more the next day. You can't just take all the vitamins at once and never need them again, and if you kept taking vitamins all day it would be at best pointless, at worst dangerous) .
posted by windykites at 9:49 AM on May 27, 2013

More drug than the recommended dose does not necessarily translate to more effective; excess is often either useless or harmful. (For a topical treatment it's more likely to fall on the useless end of the scale, but I don't know where finasteride falls)

Drug doses are not arbitrary - they are determined by effectiveness relative to toxicity. Some drugs are more toxic than others, but pretty much all of them can have side effects at a high enough dose. If you could get better results without higher toxicity by increasing the dose, that higher dose would be the recommended one in the first place.

Finasteride works by inhibiting the conversion of testosterone into a more active form, which can contribute to hair loss. So there is only so much inhibition that can happen, particularly since there are alternative ways for the active testosterone to be produced.
posted by randomnity at 10:30 AM on May 27, 2013 [1 favorite]

If you could get better results without higher toxicity by increasing the dose, that higher dose would be the recommended one in the first place.

Yes, and also if they could sell more product by recommending you use more or use it more often, they almost certainly would.
posted by fiercecupcake at 11:13 AM on May 27, 2013

My drug information resources say that "more frequent use of or using more Rogaine (minoxidil) than indicated will not improve results." Basically you're taking 2 doses of the topical medicine per day and any more than that will either cause negative side effects or won't help.

In order for most topical meds to work they must be absorbed at least into the deeper layers of the skin, so the "wet" appearance of them on the skin is not an indication of it working more.
posted by eldiem at 2:04 PM on May 27, 2013

This is a little like asking why you don't take pills every 5 minutes instead of twice a day as directed. Rogaine is not necessarily like... moisturizer or something. Think of it like medicine that's absorbed through the skin instead of the stomach.
posted by RustyBrooks at 4:13 PM on May 27, 2013

The term that comes into play here is "Dose Response Curve". Once you've done all the things your drug does - block receptors, activate receptors, bind cytokines - whatever - that's it. You're pretty much done. Adding more doesn't really buy you anything once you reach that flat line up top.

Imagine you had 16 cups sitting on your table - trying to put more than a gallon of water in them is just going to make the kitchen floor wet. Similarly, adding more water every 15 minutes to keep up with evaporation (in drug metabolism it's called half-life, but the idea holds) is kind of pointlessly excessive.

And, as has been noted, adverse effects due to excessive dosing is a thing.
posted by Kid Charlemagne at 7:21 PM on May 27, 2013

fiercecupcake: If you could get better results without higher toxicity by increasing the dose, that higher dose would be the recommended one in the first place.

Yes, and also if they could sell more product by recommending you use more or use it more often, they almost certainly would.

Which the OP has already pointed out he understands, so let's move on to his actual question.

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First: don't confuse "dry" with "not in liquid". Your skin is perpetually covered in oils; many meds are oil-soluble.

Second: if the mechanism by which Rogaine works can be "saturated", then obviously increasing the dosage beyond this point will never increase its effectiveness.

Consider Selective Serotonin Reuptake Inhibitors - SSRIs, a common anti-depressant. They work by blocking the chemical sites that are waiting to catch a serotonin molecule, which takes that "relax/feel-good/don't-worry" brain chemical out of commission. If your brain has a million of these sites, and your dosage has covered all one million of them, you can't get any better than that.

I don't know how Rogaine works, but this sort of model seems to make sense for a usage prescription that claims "using it more often won't improve results."
posted by IAmBroom at 12:15 AM on May 28, 2013