Molecular Weight (Skincare)
Molecular Weight (Skincare) — the size of an ingredient's molecule, expressed in daltons, which strongly influences how readily it can pass through the skin's outer barrier. As a general rule, smaller molecules penetrate more easily, while larger ones tend to remain on the surface. This concept helps explain why the same ingredient can behave differently depending on its molecular form.
Key points
- Molecular weight is measured in daltons and reflects the mass and roughly the size of a molecule.
- A commonly cited guideline suggests molecules under about 500 daltons penetrate skin more readily than larger ones.
- Hyaluronic acid is a familiar example, available in high- and low-molecular-weight forms that sit on or penetrate skin differently.
- Molecular weight is only one factor in absorption, working alongside solubility, charge, and the surrounding formula.
Frequently asked
Does a lower molecular weight always mean better results?
Not necessarily, because deeper penetration is only useful if the ingredient is meant to act below the surface, and smaller size can also increase irritation potential.
What is the 500 dalton rule?
It is a general guideline suggesting that molecules smaller than roughly 500 daltons are more likely to penetrate the skin barrier, though it is an approximation rather than a strict cutoff.
Related topics
This is a foundational entry in the SYNC Skin Encyclopedia and is expanded over time. Educational information only — not medical advice.
