Claims are only as strong as the evidence behind them. The choice of clinical vs. in vitro testing generates different types of evidence, and that difference shapes what conclusions can be drawn about product performance and how confidently those conclusions can support a claim. This distinction matters most for teams comparing formulation testing methods early in a product’s life cycle, before a claim is ever written.
Important Context
According to the FTC’s Health Products Compliance Guidance, clinical testing isn’t required for every claim — the appropriate level of substantiation depends on the claim itself. But for objective efficacy claims, appropriately designed human clinical studies generally provide stronger substantiation than in vitro studies alone, because they evaluate the finished product in its intended users. This article is intended to provide scientific context and does not constitute legal or regulatory advice.
How Testing Strategy Shapes Product Outcomes
Testing methods determine the type of evidence available for product decisions and claims.
Different Testing Methods Answer Different Questions
Different testing approaches measure different aspects of product performance:
- In vitro testing focuses on biological activity under controlled conditions.
- Clinical testing evaluates how products perform under real conditions, with real users.
- Testing strategy influences what claims can be supported — and how confidently those claims can be communicated.
For teams still exploring a mechanism, that often starts with a Clinical Research Studies engagement — earlier-stage, proof-of-concept work that sits ahead of a full claims study.
Understanding the Evidence Hierarchy
Not all evidence contributes the same level of support for product claims.
| Evidence type | Typical endpoints | Supports consumer-facing claims* | Relative strength* |
| Literature review | Published scientific evidence | Limited | Low |
| In vitro testing | Cell assays, reconstructed skin, microbiome models | Limited | Low–Moderate |
| Ex vivo testing | Human skin explants | Limited–Moderate | Moderate |
| Human clinical study | Self-assessment, dermatologist grading, objective measurements (e.g. TEWL, imaging, microbiome profiling) | Yes | High |
| Randomized, controlled human clinical study (when appropriate) | Same endpoints, with more rigorous design | Yes | Very High |
*Illustrative only. The appropriate substantiation depends on the specific claim, product category, and regulatory context.
As evidence moves down this table, it becomes more product-specific and more capable of supporting a consumer-facing claim. Ex vivo testing sits in between in vitro and clinical: skin explants add human tissue context without yet testing a finished product on real users. The value of any piece of evidence for cosmetic claims validation depends on what it can actually demonstrate about the product being evaluated.
What In Vitro Testing Reveals
In skincare and other personal care categories, in vitro testing typically comes first. It helps identify biological responses and potential mechanisms.
– Measures cell- or tissue-level responses in a controlled lab setting.
– Can evaluate microbiome responses, ingredient interactions, and biological effects.
– Useful during formulation development and early-stage product evaluation.
What It Leaves Unanswered
Laboratory results do not automatically translate into product performance.
– Biological activity does not necessarily confirm measurable product outcomes.
– Additional validation may be needed to understand whether observed effects translate into claim support.
In vitro testing helps explain how a product may interact with biological systems — not necessarily how that product performs in practice
What Clinical Testing Adds to Claim Substantiation
Assessing Finished-Product Performance
This is where product performance validation actually happens — the finished product gets put in front of its intended users, not just an isolated ingredient or mechanism.
– Measures outcomes directly in participants.
– Can incorporate instrumental measurements, dermatologist grading, and participant feedback.
– Evaluates product performance rather than biological activity alone.
Where microbiome profiling fits: Microbiome profiling isn’t a separate level of evidence on its own — it’s an objective biomarker built into a human clinical study, alongside dermatologist grading and instrumental measurements. It’s also the biomarker that matters most here: it’s what lets a brand see not just whether a product works but how it’s shaping the skin microbiome in real users.
Connecting Product Outcomes to Claims
For skincare brands and manufacturers, clinical testing is where claim substantiation for skincare products actually gets made. It helps determine whether observed outcomes support the intended claim.
– Links product performance to claim development.
– Provides evidence generated under real-use conditions.
– Can strengthen confidence in market-facing communication.
Clinical testing supports claims by generating measurable outcomes under real conditions, as demonstrated in Clinical Claims Studies designed for cosmetic claims validation.
That real-use layer is what closes the gap between a lab signal and a claim. This is reflected in a clinical study with OneSkin, in which clinical microbiome testing was used alongside standard clinical endpoints to validate product performance and substantiate claims in real-world use. Without this layer, results remain disconnected from real performance — signals that appear strong in controlled settings don’t always hold in real use.
Why Results Do Not Always Support the Intended Claim
Testing results are often treated as direct evidence for a claim, but they don’t automatically confirm it. Regulators evaluate the net impression an advertisement makes on consumers — not just the individual words or disclaimers used to qualify it. That’s why the type of evidence behind a claim carries real weight: even compelling lab data or positive clinical results aren’t, on their own, a claim.
Take a claim like “supports microbiome diversity” — a cell-based assay might show an ingredient acts on a target microbe. Still, that alone doesn’t establish that the finished product measurably shifts diversity on real skin.
Regulators frame that same gap as a substantiation risk, and how much risk depends on the evidence behind the claim:
| Scenario | Substantiation risk* | Why |
| Claim supported only by in vitro testing | Highest | In vitro studies may show biological mechanisms but generally don’t establish that a finished product produces the claimed effect in people. |
| Product advertised as “in vitro tested” where consumer efficacy is implied | Moderate–high | A technical qualifier may not offset the overall impression that the product has been shown to work on people. |
| Claim supported by an appropriately designed human clinical study | Lower | Human studies evaluate the finished product directly in its intended users. |
*Illustrative only — actual risk depends on the specific claim, evidence, and regulatory context.
In vitro testing remains valuable mechanistic evidence, and it often complements clinical data. Per the FTC’s Penalty Offenses Concerning Substantiation, the risk arises specifically when a consumer-facing efficacy claim rests primarily on non-human evidence while implying the benefit has been shown in people. That’s the standard that defensible claim validation is meant to meet.
Choosing the Right Evidence for Your Claim
How a team approaches clinical vs. in vitro testing shapes the evidence available for product performance validation and claims development. A claim like “helps maintain microbiome diversity” only holds up when the evidence behind it actually measured the microbiome — in the finished product, in real users.
Support your claims with evidence that reflects real product outcomes.