Growth factors in topical and injectable products

The biology is the easy part

Growth factors are among the best characterised signalling molecules in biology. Families relevant to skin include those involved in fibroblast activity, epithelial growth, vascular development and matrix regulation. They bind specific receptors, initiate intracellular signalling cascades, and change what the cell does.

Their role in wound healing is established. A wound produces a sequence of signalling events in which different factors dominate at different stages, and the sequence matters as much as the inventory. Applying a fixed mixture to skin is not the same input as a tissue generating its own sequence in response to its own state.

Four practical obstacles

Size

Proteins are large molecules by the standard that governs topical penetration. Intact stratum corneum restricts them severely, for the reasons set out in can a vesicle cross the skin barrier. A growth factor in a cream faces the same barrier problem as a vesicle, in lesser degree but the same direction.

Stability

Proteins denature. Temperature excursions, pH changes and time all degrade activity, and a denatured protein may still be detected by an assay that recognises a fragment of its sequence while having lost its function entirely. Detection and activity are not the same measurement, which is a recurring theme on this site.

Concentration window

Signalling systems frequently have optimum ranges rather than monotonic dose responses. More is not reliably better and can be worse. A product formulated to maximise a number on a label is not necessarily formulated to hit a useful concentration at the target.

Sequence

Tissue repair is a timed programme. A single application delivers a snapshot of a sequence. Whether that produces a coherent response, an incoherent one, or nothing at all is an empirical question rarely posed in product literature.

A topical product containing growth factors improves dermal collagen in human skin.

Proposed mechanism

Applied growth factors reach dermal fibroblasts and bind receptors, increasing matrix synthesis.

What has been shown

Growth factor signalling in fibroblasts is well established in laboratory systems. Topical products in this category have been studied clinically, mostly in small studies with appearance-based endpoints. Evidence that applied growth factors reach dermal fibroblasts in active form through intact skin, at a concentration capable of receptor engagement, is the step we cannot point to.

Highest level reached

Small human studies

Main confounders

Vehicle effects, since a well formulated moisturiser improves the appearance of skin on its own. Denaturation between manufacture and application. Appearance endpoints without histology. Concurrent use of other actives.

GradePLAUSIBLE, UNTESTED

What would change thisA vehicle-controlled trial in which the vehicle is identical minus the growth factor, with an objective endpoint and, ideally, evidence of the molecule reaching the dermis in active form. The vehicle arm is the essential part, because the vehicle alone is expected to improve appearance.

Where growth factors come from in these products

Three sources are used and they carry different questions.

• Recombinant production. A defined protein produced in a cell system and purified. This is the most controllable option: identity and quantity are specifiable, and the material can be characterised properly.
• Cell-derived mixtures. Conditioned medium or its fractions, containing whatever the cells released. Composition is not fully defined and varies with culture conditions.
• Platelet-derived. Released from the patient's own platelets, as in the preparations covered in PRP and PRF.

A product using recombinant material can tell you exactly what is in it. A product using cell-derived material generally cannot, and a growth factor panel run on such a preparation reports what was detected in that batch, not a specification the next batch will meet.

The injectable question

Injecting a growth factor preparation into skin bypasses the barrier and changes the question entirely. It also changes the regulatory frame: a product presented as acting pharmacologically on the body, administered by injection, sits squarely within the territory covered in borderline products and the MHRA. The fact that a product can be purchased does not establish that it may lawfully be injected. Check the primary sources, not a supplier summary.

What the category is good at

It would be unbalanced to leave this without saying what the plausible benefits are. Well formulated topical products in this category are generally also well formulated moisturisers, delivered in vehicles designed for skin, and a good vehicle improves the appearance of skin measurably. That effect is real and it is not nothing.

The question is attribution. If the vehicle is doing the work, the price premium attached to the active is buying a story rather than a mechanism. A vehicle-controlled trial would resolve it, and its absence across most of the category is the fact a careful reader should hold onto.

A short reading protocol

For any growth factor product, ask: which factors, from what source, at what stated concentration, with what stability data, and compared against what vehicle in what trial. Five questions. Products that answer all five exist and are worth taking seriously. Products that answer none are selling a molecule name.

Questions readers ask

Do growth factor creams work?

Well formulated products in this category generally improve the appearance of skin, as good moisturising vehicles do. Whether the growth factor content contributes beyond the vehicle has not been established for most products, because vehicle-controlled trials are uncommon in the category.

Can a protein penetrate skin?

Intact stratum corneum severely restricts large molecules, and proteins are large by that standard. Penetration in useful quantity through intact skin is not established for growth factors, which is why many protocols pair them with barrier disruption.

Is recombinant better than cell-derived?

Recombinant material can be specified and quantified precisely, which is an advantage for consistency. Cell-derived mixtures contain a broader and less defined set of molecules, which some argue is closer to physiological signalling and which makes batch specification harder.

Does more growth factor mean better results?

Not reliably. Signalling systems often have optimum concentration ranges rather than simple dose responses, so higher concentrations are not automatically better and can be less effective.

Why does the vehicle matter so much?

Because a well designed cosmetic vehicle improves skin appearance on its own through hydration and barrier support. Without a vehicle-only comparison arm, an improvement seen with the full product cannot be attributed to the active ingredient.