Conditioned media and the secretome
What conditioned culture medium is, what the secretome includes, and why many products described as exosome products are better described as secretome concentrates.
Conditioned medium is the liquid a cell culture has been grown in, collected after the cells have had time to release material into it. The secretome is the full set of molecules a cell releases, including free proteins, lipids, metabolites and extracellular vesicles.
Most commercial preparations in regenerative aesthetics begin as conditioned medium. What distinguishes one from another is how much of the non-vesicular fraction was removed, and how well that removal was demonstrated. A product marketed on the vesicle name but purified only lightly is, functionally, a secretome concentrate.
The simplest description of how these products are made
Cells are grown in a nutrient liquid. Over time they release material into it. The liquid is collected, cleared of cells and debris, concentrated, and either used as is or subjected to further separation to enrich for a fraction of interest. That is the entire manufacturing logic behind a large share of the category.
What varies is the last step. A product may be:
- Concentrated conditioned medium, with cells and large debris removed and the liquid reduced in volume.
- Fractionated conditioned medium, with an additional separation step intended to enrich for particles in a size or density band.
- A purified vesicle preparation, with orthogonal steps and characterisation demonstrating what was enriched and what was depleted.
All three can legitimately be described as derived from cells. Only the third supports a specific claim about vesicles, and the third is the most expensive and lowest yielding to produce. That economic reality shapes the market more than any biological consideration.
What else is in the liquid
A crucial and under-discussed point: conditioned medium is not a blank canvas that cells write on. It starts as a formulated nutrient solution, and if serum was used, it starts with a very large quantity of protein, lipoprotein particles and serum-derived vesicles already present.
Serum-derived material overlaps in size and density with the material a manufacturer is trying to isolate. That is why serum-free or vesicle-depleted culture conditions matter, and why the culture protocol belongs in any assessment of a product rather than being treated as a background detail. A preparation grown in ordinary serum-supplemented medium and isolated by a size-based method will contain serum-derived particles whose contribution nobody has measured.
A preparation sold on the vesicle name derives its biological activity from the vesicles it contains.
- Proposed mechanism
- Vesicles isolated from conditioned medium carry cargo that acts on recipient cells.
- What has been shown
- Preparations of this kind have produced effects in cell culture assays in many published reports. Attribution of those effects to the vesicle fraction specifically, as opposed to co-isolated soluble protein, lipoprotein or residual medium components, requires depletion or fractionation controls that are frequently absent from the reports offered in support of commercial products.
- Highest level reached
- In vitro only
- Main confounders
- Serum-derived particles and proteins if serum was used. Residual medium components with biological activity of their own. Concentration steps that enrich everything, not only vesicles.
GradePLAUSIBLE, UNTESTED
What would change thisA comparison, in the same assay, between the full preparation, the vesicle-depleted supernatant, and vesicle-free medium taken through identical processing. If activity tracks with the vesicle fraction and disappears from the depleted fraction, the attribution is earned.
Why the word secretome is more precise
The secretome is everything a cell releases. It includes conventional secreted proteins such as growth factors and cytokines, extracellular matrix components, lipids, metabolites and vesicles. Describing a preparation as a secretome fraction is often the most accurate statement available, and it is a perfectly respectable description of a product.
It also changes which questions matter. If the active principle may be a free growth factor, then protein stability, protease exposure and skin penetration for a soluble protein become the relevant questions, and vesicle-specific concerns about membrane integrity become less central. Different active principle, different failure modes, different handling requirements. A manufacturer who has not decided which they are selling cannot have designed rational handling rules.
| Description | What is asserted | What must be shown |
|---|---|---|
| Conditioned medium concentrate | Cells released material into liquid, which was concentrated | Cell identity, culture conditions, sterility, absence of cells |
| Secretome fraction | A defined subset of released material was retained | The above, plus what the fractionation removed and retained |
| Extracellular vesicle preparation | Vesicles are present and enriched | The above, plus particle characterisation, marker profile, particle to protein ratio, and depletion of non-vesicular material |
The regulatory relevance
How a preparation is described bears on how it is likely to be classified. A material derived from human cells raises human tissue questions. A material presented as acting pharmacologically on the body raises medicines questions. A material presented as a cosmetic raises cosmetic regulation questions, with its own restrictions on ingredients and claims. These are not alternatives a supplier gets to choose freely: classification follows from what the product is and how it is presented.
We set out the UK position in the UK position on exosome products, the classification test in borderline products and the MHRA, and the tissue dimension in human tissue considerations. Nothing on this page should be read as legal advice, and the primary sources are linked at the foot.
Does any of this make conditioned media uninteresting?
No. Conditioned medium is a serious research tool and there is a substantial literature on the biological activity of secretomes from various cell types in laboratory models. The interest is genuine.
The problem is specifically the mismatch between what a preparation is and what it is called. A product that says "secretome concentrate from a defined cell source, characterised as follows" is making a claim it can support. The same product marketed as an exosome therapy is making a narrower claim it usually cannot. The material has not changed. The evidential position has.
A practical reading test
Given a product document, look for three things in order. First, does it name the cell source and the culture medium, including whether serum was used and whether it was vesicle depleted? Second, does it state the separation method by name rather than by trade description? Third, does it report what was measured after separation, including at least one measure of purity such as a particle to protein ratio? A document that answers all three is describing a manufacturing process. A document that answers none is describing a category and attaching a price to it.
Questions readers ask
Is conditioned medium the same as an exosome product?
Conditioned medium is the starting material. An exosome product is meant to be a purified fraction of it. Whether a given commercial product is closer to one or the other depends on the separation steps used and what characterisation was performed.
What is the secretome?
Everything a cell releases, including free proteins such as growth factors and cytokines, lipids, metabolites, matrix components and extracellular vesicles. It is often the most accurate word for what is in these preparations.
Why does serum in the culture medium matter?
Serum contributes large amounts of protein, lipoprotein particles and its own vesicles, which overlap in size and density with the material being isolated. Unless serum-free or vesicle-depleted conditions were used, some of what is in the final vial came from the serum, not the cells.
Is a secretome product inferior?
Not necessarily. It is a different product with a different likely active principle and different handling requirements. The problem is a product being sold under one description while being manufactured to another.
How can I tell which one a product is?
Look for the separation method named specifically, and for a purity measure such as particle to protein ratio. Concentration alone, with no fractionation step described, indicates a conditioned medium concentrate.