A: No – not everything you put on your skin will make its way inside. Skin absorption is selective about what is allowed in and what is kept out.
To understand how the absorption of chemicals through the skin is determined, we need to go back to the beginning of life on land.
Eons past, when plants and animals left the watery confines of the sea to inhabit the dry land, they had to devise a means to hold onto the water in their cells – for all living cells are a water-based system. They had to prevent its evaporation into the drier atmosphere that now surrounded them. The near-universal solution to this dilemma was to develop a covering or ‘integument’ that could prevent the loss of precious internal water.
It is our skin’s permeability barrier that allows us to be ‘grapes’, and not ‘raisins’. It also prevents us from ballooning into ‘watermelons’ when we bathe or swim.
Thus, our skin was designed by evolution to hold our body’s water inside, to prevent it from evaporating away, like water from a shallow bowl. And all of these integumental barriers – whether on plants or animals – use a coating of water-unfriendly materials (or ‘lipids’) to seal off their watery interiors from a desiccating environment outside. The differences between the barrier systems of a leaf or an insect or of humans lie only in the details of their lipid-based barrier systems.
The Basic Principles of Skin Absoption
[Read more…] about Q: I’ve heard that anything you put on your skin can get absorbed. Is that true? Should I be worried about this?
Because our skin’s barrier was designed to prevent water-movement, it follows that small, water-friendly molecules – ones that readily dissolve in water (like sugar or salts) – are also prevented from moving in or out of the skin. Thus, for example, we don’t become salt-intoxicated when we swim in the ocean.