Dalton 500 & Collagen
The Doltons 500 rule states that the maximum molecular weight of a molecule that can be absorbed through the skin is 500 Daltons. This means that collagen molecules are too large to be absorbed through the skin, and therefore must be broken down into smaller molecules for the body to be able to absorb them. This is why collagen supplements are often taken orally, as the molecules can be broken down in the digestive tract and then absorbed into the bloodstream.