: Why can the human body absorb toxins thru the skin, but you can’t rehydrate yourself by sitting in water?
In: Biology
So a large bulk of your skin is made up of keratin, a long fiberous protein. Imagine it weaving together like a woven basket. There’s still gaps in those woven threads however, so your skin has a layer of fat around and between the weaves of keratin. Water doesn’t dissolve into fat, so that layer of fat makes for a particularly effective barrier to prevent water from slipping through the keratin threads and into your body.
Some toxins however *can* dissolve into fats (like, for example, mercury). And on contact with your skin *those* chemicals dissolve into the fatty layer between the keratin weave and slip through.
So the human body doesn’t absorb “toxins” through the skin, but it can absorb *some* toxins, mainly those that are good at dissolving into fats.
Long and short, toxins can broadly be classifed as “water-soluble” and “fat-soluble” broadly, meaning “can be dissolved in water” and “can be dissolved in fat”.
Water is not fat-soluble. Meaning the fatty layer between the keratin bands will repel water. Some toxins *but not all* are fat-soluble (lead, mercury, certain pesticides, some drugs like fentanyl) meaning they can be dissolved into the fatty layer on your skin. If it’s not a fat-soluble toxin, then it can’t be absorbed by your skin because the fatty layer blocks it, just like it blocks water.
If nothing else – volume. Most of the toxic substances you have to worry about are toxic in very very small amounts. You lose more water while breathing out than would be more than you absorb.
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Random tangent: in an *emergency* situation, you can hydrate sitting in water (salt water, brackish water, etc). However, the water is not penetrating the skin so much as wicking into your colon via a towel / strip of cloth.
The surface of the skin has a layer of fat. When you add water to the oil, the water stays separated from the oil, so it doesn’t cross the skin’s barrier. Furthermore, some toxins have a pH at which they are easy to “dissolve”.
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