Is an exosome a cell?

No. It is not a cell but a tiny membrane-bound vesicle released by a cell. It does not replicate itself.

How big is an exosome?

Typically around 30–150 nanometres in diameter.

Are exosome products an approved treatment?

No. There is no FDA-approved exosome therapy in the United States, and the FDA has warned consumers about unapproved products.

How can I judge the quality of exosome research?

Check whether the isolation method, characterisation and purity are disclosed in line with ISEV's MISEV guidelines.

What is the difference between an exosome and an extracellular vesicle?

Extracellular vesicle is the umbrella term; exosome is the small, roughly 30–150 nm subset understood to arise from the endosomal pathway. When origin cannot be demonstrated, ISEV recommends the term “small EV”.

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Explainer

Exosomes, explained.

What extracellular vesicles are, why researchers study them, and what the evidence does and does not currently support.

The short answer

Exosomes are small extracellular vesicles — membrane-bound particles roughly 30–150 nanometres across — that cells release to carry proteins, lipids and nucleic acids to other cells. Researchers study them as a mechanism of cell-to-cell signalling and as a possible delivery vehicle. The international standard for reporting such research is MISEV, published by the International Society for Extracellular Vesicles. In the United States, exosome products are not approved by the FDA for treating any condition, and the FDA has issued consumer warnings on unapproved exosome and stem cell products.

Key takeaways

An exosome is a membrane-bound extracellular vesicle (EV), roughly 30–150 nm in diameter.
It carries proteins, lipids and nucleic acids such as mRNA and microRNA, and is understood to take part in cell-to-cell signalling.
When endosomal origin cannot be demonstrated, ISEV recommends the operational term “small EV”.
MISEV is the international reporting standard. Without isolation method, characterisation and purity, claims cannot be compared.
In the United States, exosome products are not FDA-approved to treat any disease.

The definition

An exosome is a type of extracellular vesicle (EV), roughly 30–150 nanometres in diameter. It is enclosed in a lipid bilayer and carries proteins, lipids and nucleic acids such as mRNA and microRNA.

Nanometres are hard to picture, so here is a comparison. One nanometre is a billionth of a metre. A human red blood cell is about 7,000 nm across, which makes an exosome somewhere between one-fiftieth and one-two-hundredth of that. This is why exosomes cannot be seen in a light microscope and require electron microscopy or particle-analysis instruments.

Four elements that make up the definition:

Origin: actively released by a cell — not cellular debris
Structure: enclosed in a lipid bilayer
Size: broadly 30–150 nm
Cargo: proteins, lipids and nucleic acids such as mRNA and microRNA

Is an exosome alive?

No. It is not a cell, so it neither metabolises nor replicates. It is closer to a parcel carrying whatever the parent cell packed into it, and it cannot multiply on its own.

Figure 1 — Size of extracellular vesicles

Sizes are representative reported ranges; the distribution depends on the isolation method. Diameter alone does not establish endosomal origin.

Why they are studied

Cells do not work alone; they exchange information. Exosomes are understood as one of the vehicles for that exchange, and are studied both to understand signalling in the body and as a possible way to deliver material to specific cells.

How they relate to culture supernatants

The supernatant left after cells are cultured contains the growth factors and cytokines those cells secreted, along with extracellular vesicles including exosomes. Most products labelled as containing exosomes therefore derive from a supernatant or a fraction of one.

The reporting standard

Research on extracellular vesicles has an international reporting standard: the MISEV guidelines from the International Society for Extracellular Vesicles. They require disclosure of isolation method, characterisation and purity. Claims that do not meet them cannot be compared scientifically.

What the evidence does not support

In the United States, exosome products are not FDA-approved to treat any disease, and the FDA has published consumer warnings about unapproved exosome and stem cell products. BIOT makes no medical efficacy claim for its products.

Exosome, extracellular vesicle, microvesicle: which word is correct

“Extracellular vesicle” (EV) is the umbrella term for membrane vesicles released by cells. “Exosome” refers to a small subset — about 30–150 nm — understood to originate from the endosomal pathway. “Microvesicle” refers to larger vesicles that bud directly from the plasma membrane. Because routine methods rarely prove endosomal origin, ISEV recommends the operational term “small EV” when origin cannot be demonstrated. A product label that says “exosome” therefore often describes a small-EV fraction.

A reader's checklist: five things to look for in a specification

Dictionary definitions and review papers do not tell you how to read a supplier's document. These five items can be applied directly to any specification sheet.

A label that omits items 2 and 3 does not meet MISEV reporting requirements and cannot be compared scientifically with any other product. Where all five are present, the material can be assessed on its own terms, independently of any efficacy claim.

1. Starting material — is the cell type, tissue origin and donor information identified?
2. Isolation method — is it stated (ultracentrifugation, size-exclusion chromatography, precipitation)?
3. Characterisation — are particle size distribution, particle count and marker proteins reported?
4. Purity — is it expressed as a ratio, such as particles per unit of total protein?
5. Storage and transport — are the temperature range and shelf life defined?

Read: the science of culture supernatants ISEV / MISEV guidelines Browse the Knowledge Hub

Frequently asked questions

Is an exosome a cell?: No. It is not a cell but a tiny membrane-bound vesicle released by a cell. It does not replicate itself.
How big is an exosome?: Typically around 30–150 nanometres in diameter.
Are exosome products an approved treatment?: No. There is no FDA-approved exosome therapy in the United States, and the FDA has warned consumers about unapproved products.
How can I judge the quality of exosome research?: Check whether the isolation method, characterisation and purity are disclosed in line with ISEV's MISEV guidelines.
What is the difference between an exosome and an extracellular vesicle?: Extracellular vesicle is the umbrella term; exosome is the small, roughly 30–150 nm subset understood to arise from the endosomal pathway. When origin cannot be demonstrated, ISEV recommends the term “small EV”.

Sources

* This article is provided for general scientific information. It is not medical advice, diagnosis, or treatment, and it does not warrant the efficacy of any specific product.

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