What does hypotonic mean?
Hypotonic is a technical adjective most often used in biology, chemistry, and medicine to describe a solution or fluid with a lower osmotic pressure than the liquid or tissue surrounding it. In a hypotonic environment, water moves into cells by osmosis, often causing them to swell. The word can also describe abnormally reduced muscle tone, particularly in medical writing. Its opposite is hypertonic, which has a greater osmotic pressure, while isotonic means that the osmotic pressure is equal on both sides of a membrane. Understanding hypotonic is important for interpreting laboratory procedures, cellular physiology, intravenous fluid treatment, and clinical assessments involving fluid balance.
Having a lower osmotic pressure than the surrounding solution or fluid.
"The sample became hypotonic after excess water was added."
Common in biology, chemistry, and medicine; often paired with solution, fluid, medium, or environment.
Having abnormally reduced muscle tone.
"The examination revealed hypotonic limbs and delayed reflexes."
A clinical and physiological sense, less common than the osmotic-pressure meaning.
A hypotonic environment can make a cell swell, which is why IV fluids with carefully controlled tonicity are essential in medicine.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does hypotonic come from?
Hypotonic was formed within English from the combining form hypo-, meaning “under” or “below,” and tonic, relating to tension or osmotic pressure. The roots Greek hypo- and tonikos, associated with stretching or tension, supplied the underlying terminology. Its development followed the related scientific terms hypertonic and isotonic, which use the same tonic element in contrasting ways.
How hypotonic is actually used
In biology, chemistry, and medicine, the word is technical and usually contrasts with hypertonic or isotonic conditions. Its physiological sense is less common and is chiefly used in clinical descriptions.
Easily confused with hypotonic
A hypotonic solution has a lower solute concentration and osmotic pressure than its surroundings, whereas a hypertonic solution has a higher one.