DOK Learning Centre · 3 min read
Adsorption vs Absorption: What’s the Difference?
One letter changes the meaning entirely. Here is what each term describes and which one applies to activated charcoal.
Key takeaways
- Adsorption: molecules attach onto a surface.
- Absorption: a substance enters and mixes into the bulk of another material.
- Activated charcoal works primarily by adsorption, on its porous surface.
Adsorption — sticking to a surface
In adsorption, molecules attach to the outside of a material. Nothing is soaked in; the interaction happens at the surface. With activated charcoal, that surface is the vast internal pore network of the powder.
Absorption — soaking in
In absorption, a substance passes into the body of another material and mixes with it — water soaking into a sponge, or a nutrient being taken up through the gut wall into the bloodstream.
Why the distinction matters here
Activated charcoal is not taken up by the body. It passes through the gastrointestinal tract, and substances that have adsorbed onto its surface travel with it.
In appropriate clinical contexts, this means activated charcoal can adsorb some substances present in the gastrointestinal tract and reduce how much of them is available to be absorbed by the body. Which substances, and how effectively, varies a great deal — activated charcoal does not bind everything.
Safety note. Because adsorption can also involve oral medicines, ask your pharmacist or clinician before using activated charcoal alongside any medication.