Medicine & Health
How does dialysis work?
Dialysis works by filtering waste and excess fluid from the blood when the kidneys can't. Blood is passed across a special membrane with cleansing fluid on the other side, and waste crosses over by diffusion — doing the kidney's job artificially.
See it in motion.
Watch a 2-minute animated lesson that shows exactly how dialysis works.
Step by step
- 1Healthy kidneys filter waste and extra water from blood; dialysis replaces that when they fail.
- 2In hemodialysis, blood flows through a machine past a semi-permeable membrane.
- 3Waste molecules diffuse from the blood into a cleansing fluid (dialysate) and are carried away.
- 4Excess fluid is also drawn off, and the cleaned blood returns to the body.
- 5Peritoneal dialysis instead uses the lining of the abdomen as the natural filter.
Frequently asked questions
- Why do people need dialysis?
- When the kidneys lose most of their function (kidney failure), waste and fluid build up dangerously. Dialysis removes them artificially to keep the person well.
- How does waste actually leave the blood?
- By diffusion: waste is concentrated in the blood and nearly absent in the cleansing fluid, so it naturally moves across the membrane from high to low concentration.
- Is dialysis a cure?
- No — it replaces lost kidney function but doesn't heal the kidneys. It's ongoing treatment unless the person receives a kidney transplant.