Can a vesicle cross the skin barrier?
The stratum corneum as a size barrier, what is known about nanoparticle penetration, and why route of application is the central unanswered question.
The outermost layer of skin is a dense, lipid-rich barrier whose function is to prevent exactly this kind of passage. General dermatological understanding is that intact stratum corneum severely restricts penetration of large molecules and particles, and vesicles are very large by that standard.
This is why almost every clinical use of these preparations is paired with a barrier-disrupting procedure. It also means the interesting question is not whether the material crosses intact skin, which is unlikely, but how much crosses disrupted skin, how deep it goes, and whether it is still intact when it gets there. Those questions are, as far as we can establish, not well answered in published work for any commercial preparation.
What the barrier is
The stratum corneum is the outermost layer of the epidermis: flattened, non-living cells embedded in a lipid matrix, arranged in a structure often compared to brick and mortar. Its evolutionary job is to keep water in and keep foreign material out. It is very good at both.
Dermatological understanding of topical delivery has long held that passage across intact stratum corneum is strongly restricted by molecular size and influenced by how a molecule partitions between water and lipid. Small, moderately lipophilic molecules can cross. Large hydrophilic molecules generally do not, in useful quantities. Proteins are already large by this standard. Vesicles are larger again, by a wide margin.
The size argument, stated carefully
We are not going to reproduce a molecular weight cut-off as though it were a hard line, because it is a rule of thumb with exceptions rather than a physical constant. The defensible version of the argument is comparative: vesicles are orders of magnitude larger than the molecules that penetrate intact skin readily, and there is no established mechanism by which an object of that size traverses an intact lipid-packed barrier in quantity.
Appendageal routes, meaning hair follicles and sweat ducts, are a recognised partial exception because they bypass the corneal layer. Follicular delivery of particles is a real research area, particularly relevant to scalp applications. It provides a route for some material to reach some depth in some skin sites. Whether that constitutes meaningful delivery to dermal targets, and whether the material remains intact, are open questions we cannot resolve from published work.
A vesicle preparation applied to intact skin delivers vesicles to the dermis.
- Proposed mechanism
- Vesicles penetrate the stratum corneum and reach dermal cells, where cargo acts.
- What has been shown
- General dermatological understanding of the skin barrier holds that particles of this size do not cross intact stratum corneum in meaningful quantity. Follicular routes offer partial access. We are not aware of published work demonstrating intact vesicles reaching human dermis after topical application to intact skin, and we will not assert a quantity we cannot source.
- Highest level reached
- Not shown
- Main confounders
- Detection of a label in skin does not demonstrate an intact vesicle arrived. Ex vivo skin models differ from living skin in barrier integrity. Occlusion, vehicle and formulation alter penetration substantially.
GradeNOT SUPPORTED
What would change thisImaging or tracer work in human skin distinguishing intact vesicles from free label at defined depths after topical application to intact skin, with quantification, and a comparison against the same preparation after barrier disruption.
Why this reframes the whole product category
If material does not cross intact skin, then a preparation applied topically to intact skin can only act at the surface or on the upper epidermis, or not at all. That is not automatically without value, since surface hydration and barrier support are genuine cosmetic effects, but it is a very different claim from remodelling dermal matrix.
It also explains the clinical pattern. Vesicle preparations in aesthetics are almost always applied immediately after microneedling, or after an ablative or fractional device treatment, or alongside some other barrier disruption. The procedure creates channels. The preparation is applied into them. This is a rational design given the barrier, and it introduces a serious interpretive problem: the procedure has effects of its own, and separating those from any effect of the substance requires a control that most reported studies do not have. We treat that in microneedling as a delivery route.
| Route | Barrier status | Principal open question |
|---|---|---|
| Topical to intact skin | Intact | Whether anything of size reaches living tissue at all |
| Topical after microneedling | Transiently breached | How much enters, how deep, and what the needling alone would have achieved |
| Topical after fractional or ablative device | Breached, with thermal effect | The same, with an added thermal injury response confounding attribution |
| Injection into dermis | Bypassed | A different regulatory question entirely, addressed in our regulation section |
The regulatory fork
The moment a preparation is injected rather than applied, the question stops being about penetration and becomes about what is being administered into a person. That is a different legal frame, and it is the fork on which the UK position turns. We set it out in topical after microneedling is a different question. In short, do not assume that because a product is available it may lawfully be given by any route, and check the primary sources rather than trusting a summary, including ours.
Stability during the crossing
Even where a route exists, intactness on arrival is a separate question. Skin contains enzymes, the environment differs in pH and ionic composition from a storage buffer, and mechanical shear during application is not negligible. A vesicle that ruptures on the way delivers its contents as free molecules into a hostile environment, which is a different mechanism with a different expected outcome.
This is why storage and handling data matter more than they appear to. If a preparation is sensitive to freeze and thaw cycles, to temperature excursions, or to the mechanical stress of being drawn through a fine needle, the product delivered may not resemble the product tested. We cover this in sterility, endotoxin and cold chain.
What a careful position looks like
A defensible summary of the current position, in our reading, is this. Intact skin is a strong barrier to objects of this size and there is no good reason to expect meaningful transdermal delivery of vesicles through it. Barrier disruption creates a route. How much material takes that route, how deep it travels, and in what state, are not well established for commercial preparations. Any claim that depends on dermal delivery therefore rests on an unmeasured step.
That does not mean the treatments do nothing. Microneedling alone has a body of evidence behind it. It means the contribution of the applied substance is the part that has not been isolated, and that a patient told the substance is the reason for their result is being told something the published evidence does not currently support.
Questions readers ask
Can exosomes penetrate intact skin?
There is no established mechanism by which particles of that size cross an intact stratum corneum in meaningful quantity, and we are not aware of published work demonstrating it in human skin. Follicular routes may allow some access, which is a partial and incompletely characterised exception.
Why is microneedling used with these products?
Because it transiently breaches the barrier and creates channels through which material can enter. It is a rational response to the penetration problem, and it introduces a confound because needling has effects of its own.
Does that mean topical products are pointless?
No. Surface and upper epidermal effects such as hydration and barrier support are real cosmetic effects. It means claims that depend on material reaching the dermis are not supported by topical application to intact skin.
Do vesicles survive the journey?
Intactness on arrival is a separate question from penetration and is rarely addressed. Enzymes, pH, ionic environment and mechanical shear during application can all disrupt a vesicle, in which case the cargo arrives as free molecules rather than as packaged ones.
Is injection the solution?
Injection bypasses the barrier and creates an entirely different regulatory question about what may lawfully be administered into a person. Availability of a product does not establish that any route of administration is lawful. Check the primary regulatory sources.