Isotonic Vs Hypotonic

Hypotonic solutions for rapid rehydration

  • Osmolality measures the total concentration of soluble ingredients in a solutions
  • Solution osmolality can be hypertonic, isotonic and hypotonic
  • Hydralyte Sports is HYPOTONIC which means the osmolality is less concentrated than blood
  • Hypotonic solutions are considered most effective for rapid rehydration
  • Isotonic solutions (like Powerade) have the same osmolality as blood so the net effect of absorption at a cellular level is zero i.e. only passive diffusion can take place
  • Blood osmolality ranges from 280-300 mOsm/kg


The osmolality of Hydralyte Sports™ is 260 mmol/L, which is in line with the World Health Organisation’s accepted levels for an oral rehydration solution.


Hypertonic Isotonic Hypotonic
Osmolality measurement mOsm/kg Greater than 300 mOsm/kg 280 – 300 mOsm/kg Less than 280 mOsm/kg
Solution osmolality is Higher than blood Same as blood Less than blood
What happens? Fluid leaves the cell – shrinks No net effect Fluid gushes into the cell – swells
It’s just like… Putting salt on top of an eggplant Pouring water into water A sultana swelling in a glass of water