Extracellular vesicles are nanoscale particles secreted by virtually every cell type known to biology. Each particle is a small, membrane-bound sphere built around a lipid bilayer, the same kind of membrane that surrounds the cell that released it. Inside that membrane, EVs carry a cargo of proteins, lipids, nucleic acids (including miRNA and mRNA), and other bioactive molecules. When taken up by recipient cells, this cargo can influence gene expression, modulate inflammatory signalling, and support repair and regeneration processes. EVs are how cells, across animals, plants, and microorganisms, transmit functional molecular information to one another.
That single biological description hides a vocabulary problem the EV field has spent the last decade trying to clean up. The market uses "exosome" as if it were a synonym for EV. The science does not.
Three subpopulations, three biogenesis routes
The International Society for Extracellular Vesicles (ISEV) defines three principal EV subpopulations, distinguished not by size but by the cellular machinery that produces them.
Apoptotic bodies are released as cells break down at the end of their life cycle, through a process of membrane blebbing during programmed cell death. They are typically the largest of the three, ranging from roughly 1,000 to 5,000 nm.
Microvesicles, also called ectosomes, form by direct outward budding of the plasma membrane and pinch off into the extracellular space. They span an intermediate size range, roughly 100 to 1,000 nm.
Exosomes are produced through a more elaborate intracellular pathway. The process begins inside the cell with the formation of multivesicular bodies (MVBs), which are endosomal compartments that gather small vesicles internally through inward budding. When an MVB fuses with the plasma membrane, those internal vesicles are released to the extracellular space as exosomes. They are typically the smallest of the three, roughly 30 to 150 nm.
Why "exosome" almost always means something else
The term "exosome" is technically reserved for particles produced by the multivesicular body pathway. To call a preparation an exosome credibly, you have to demonstrate that biogenesis route. The standard evidence is a combination of EV-associated protein markers, including CD9, CD63, CD81, TSG101, and Alix, that confirm MVB origin, alongside data showing the absence of contaminating non-vesicular material.
Most current isolation techniques cannot cleanly separate exosomes from the other two subpopulations. They produce mixed EV preparations, with exosomes, microvesicles, and a smaller fraction of apoptotic bodies all present in the same suspension. That is the technical reality MISEV2023 was written to address: when biogenesis cannot be experimentally confirmed, the correct term is "extracellular vesicle", not "exosome."
Almost no commercial product on the market today provides marker-confirmed biogenesis data for what it sells as exosomes. The label is a shorthand the market adopted because "EV" did not test well in consumer research. The science kept the precise term and added the umbrella one. The market kept the wrong term and dropped the precise one.
What this means for clinicians and partners
Three things follow from the biology.
First, two products marketed as exosomes are not assumed equivalent without source, isolation, and characterization data. Source determines what cargo the EV carries. Isolation method determines which subpopulations dominate the final suspension and how much non-vesicular material rides along. Characterization data determines whether the count on the label corresponds to actual EV-range particles or to a broader nanoparticle population.
Second, particle concentration on a Certificate of Analysis is meaningful only when the analytical method is named. Nanoparticle Tracking Analysis (NTA) is the gold standard under MISEV2023. A "particle count" produced by another method, or no method at all, does not carry the same evidentiary weight.
Third, the precise term to use in formal scientific or clinical writing is "extracellular vesicle" or "EV." In product copy aimed at clinicians and consumers, the working compromise is "EV/exosome" together, which is what we use across BioThera communications. It bridges scientific precision with the language already in use without privileging the marketing convention over the science.
The downstream consequence
Every comparison clinicians and procurement teams make about EV products downstream of this point depends on the vocabulary being right at the start. Source, biogenesis, isolation, characterization. If those four are not specified, "exosome product" is a category claim, not a specification. The work of the EV field over the past five years has been to make the specification possible. The work of credible EV manufacturers is to publish it.