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Originally Posted by Molasar
Clodfobble my science education was a long time ago but aren't transdermal products formulated in low molecular weight versions because big complicated molecules can't get through the skin - like you can put sand through a strainer but not gravel.
or am I talking bollocks again?
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It's true that absorption rates of larger molecules is reduced, so some medicines are not considered good candidates to get the right dose in the right amount of time, though all the vitamins have a relatively simpler structure compared to most meds. Absorption rates are also affected by how much is already in your body--swab iodine on the skin of someone who is iodine-deficient, and it will disappear within just a few hours; swab it on someone who gets enough iodine, and the brown stain will remain for 24+ hours.
There are some substances that we
believe are too large to ever fit through external skin, such as gluten, for example. However, millions of celiacs have both reported and measured symptoms of internal exposure when they only received an external dose.
It's like the mystery of how bees fly: for decades, aerodynamics experts said it was impossible, their weight plus other factors meant bees couldn't fly. Yet obviously they could. We think larger molecules shouldn't be able to get through some skin areas, but evidence shows many of them do, somehow. I'm sure we'll figure it out someday, just like
they finally figured out how bees fly.