Isotonic
Isotonic — a term describing a solution whose concentration of dissolved particles matches that inside skin cells, so it neither draws water out of nor forces water into them. In skincare formulation this balance is often sought to support comfort and minimize the osmotic stress a product places on the skin.
Key points
- An isotonic solution has a solute concentration equal to that of the cells it contacts, keeping water movement in balance.
- By contrast, hypertonic solutions can pull water out of cells and hypotonic solutions can push water into them.
- Formulating toward isotonic conditions is one way to support skin comfort and reduce irritation potential.
- The concept is borrowed from cell biology and is applied to how formulas interact with the skin's cells.
Frequently asked
Why would a skincare product aim to be isotonic?
An isotonic formula balances the concentration of dissolved particles with that inside skin cells, avoiding water being drawn out or forced in. This can help support comfort and reduce osmotic stress on the skin.
What is the difference between isotonic, hypertonic, and hypotonic?
Isotonic means equal particle concentration inside and outside the cell, hypertonic means a higher outside concentration that can draw water out, and hypotonic means a lower outside concentration that can push water in.
Related topics
This is a foundational entry in the SYNC Skin Encyclopedia and is expanded over time. Educational information only — not medical advice.
