Around 200 new skincare products are launched in Germany alone each month. Each promises visible results, youthful radiance, and the reversal of biological processes. In fact, most claims are based on no measurable foundation — and the difference between an effective product and an elaborately marketed moisturizer with no significant effect lies in the details of the formulation.

This article provides you with nine criteria to systematically evaluate skincare products. No marketing promises, no sweeping statements — but an analytical framework based on formulation science, dermatology, and clinical research.

Criterion 1 – INCI Transparency: What's really inside?

The International Nomenclature of Cosmetic Ingredients — INCI for short — is the Europe-wide binding system for declaring cosmetic ingredients. According to EU Cosmetics Regulation (EC) No. 1223/2009, manufacturers are obliged to list all ingredients in descending order of their weight percentage if their share exceeds one percent. Substances below one percent may be listed in any order.

This detail is crucial: an active ingredient that appears at the end of the INCI list is present in a concentration below one percent — often well below the threshold at which a measurable effect would be expected. In practice, this means that many products list attractive active ingredients such as hyaluronic acid, niacinamide, or peptides as a selling point on the label, while the actual amount contained is insufficient for an effect.

What you can do specifically: Read the INCI list completely and check the position of the advertised active ingredients. If a key active ingredient only appears after the preservatives (typically phenoxyethanol, ethylhexylglycerin), it is very likely in a concentration below 0.5 percent. Reputable manufacturers openly communicate active ingredient concentrations — or formulate in such a way that the positioning in the INCI list itself provides information.

Criterion 2 – Active ingredient concentrations in the effective range

Even if an active ingredient is present, its concentration determines whether it can exert a physiologically relevant effect. For the most important anti-aging active ingredients, well-documented efficacy thresholds exist, derived from clinical studies.

Retinol, in controlled studies, has been shown to demonstrably affect collagen synthesis at a concentration of 0.3 percent. Niacinamide (Vitamin B3) shows effects on pigmentation, barrier function, and sebum regulation at concentrations between two and five percent. Vitamin C (L-Ascorbic Acid) requires at least ten percent to be relevant as an antioxidant and collagen stimulator — with the formulation's pH needing to be below 3.5 to ensure penetration. Peptides like Argireline (Acetyl Hexapeptide-3) or Matrixyl (Palmitoyl Pentapeptide-4) are used in clinically studied formulations at concentrations of two to ten percent.

Hyaluronic acid is a special case: its efficacy depends not only on concentration but primarily on molecular weight. High molecular weight hyaluronic acid (over 1,000 kDa) remains on the skin surface and acts as a moisturizing film. Low molecular weight fractions (under 300 kDa) can penetrate deeper into the epidermis and activate moisture receptors there. A product containing only one molecular weight fraction consequently provides only a part of the theoretically possible benefit.

Criterion 3 – pH Stability and Formulation Chemistry

The pH value of a formulation is not a neutral parameter — it equally determines efficacy, skin compatibility, and product stability. The human skin surface physiologically has a pH value between 4.5 and 5.5. This slightly acidic acid mantle is essential for the integrity of the skin barrier, antimicrobial defense, and the activity of skin-resident enzymes.

Many active ingredients are only effective within a specific pH window. Vitamin C (L-Ascorbic Acid) must be formulated at a pH below 3.5 to pass through the epidermis in its ionized form. Retinol is relatively stable at neutral pH but loses its biological activity in strongly alkaline formulations. Exfoliating alpha-hydroxy acids like glycolic acid or lactic acid require a pH below 4.0 to exert their keratolytic effect.

A product with a pH value of 6.5 to 7.0 — as many commercially available creams have — may not support optimal active ingredient activity and, moreover, attacks the natural acid mantle. Repeated application of alkaline products can weaken the skin barrier in the long term, which paradoxically can contribute to accelerated skin aging.

Reputable manufacturers openly communicate the pH value of their formulations. If this information is missing, commercially available pH test strips or meters can provide an initial orientation — although accurate measurements in the acidic range require better instruments.

Criterion 4 – Encapsulation Technology for Sensitive Active Ingredients

Some of the most effective anti-aging substances are also among the most chemically unstable. Retinol oxidizes on contact with light and oxygen. Vitamin C degrades through oxidation — identifiable by a yellowing of the formulation. Certain peptides can be inactivated by enzymatic activity on the skin surface even before penetration.

Encapsulation technologies solve this problem by embedding the active ingredient in a protective matrix that stabilizes it until it is released at the site of action. Established systems include liposomes (phospholipid-based vesicles), nanoparticles made of biodegradable polymers, cyclodextrin inclusion compounds, and microemulsions. These systems fulfill several functions simultaneously: they protect the active ingredient from degradation, control the release kinetics, and can influence the depth of penetration.

In the INCI declaration, you can often recognize encapsulated active ingredients by additions such as "encapsulated," lecithin compounds as shell material, or nanoparticle designations (in the EU, nanomaterials must be labeled with the addition [nano]). A product containing retinol or vitamin C without describing a corresponding formulation technology should be critically evaluated regarding its actual active ingredient stability.

Criterion 5 – Clinical Studies and Efficacy Evidence

The distinction between a cosmetic claim and proof of efficacy is fundamental — and is deliberately blurred in the communication of many brands. In the EU, cosmetics are not allowed to make medical claims. What remains are cosmetic claims that may or may not be substantiated by studies.

Reliable efficacy evidence for a cosmetic product has specific characteristics: it was conducted on a sufficiently large group of subjects (at least 30, preferably over 60 people), uses randomized and, if possible, double-blind study designs, measures objective parameters (skin elasticity via Cutometer, moisture content via Corneometer, wrinkle depth via profilometry or optical coherence tomography), and compares against placebo or baseline. A period of at least eight to twelve weeks is required for visible structural changes.

Caution is advised with in-vitro studies (cell culture), which, while providing interesting mechanistic clues, do not allow a direct statement about the effect in humans. Pure consumer surveys ("87% of users reported smoother skin") without objective measurement points should also be critically evaluated — they measure perception, not effect.

Actively ask manufacturers for the studies that underpin their claims. A reputable company can either name a published study, refer to the raw material manufacturer and its study data, or make internally collected data available upon request. Evasive answers are themselves an informational signal.

Criterion 6 – Carrier Substances and Penetration Capability

An active ingredient only exerts its effect where it is needed — and most anti-aging active ingredients must penetrate the epidermis to be relevant. The carrier substance (the vehicle of the formulation) largely determines how deeply and how quickly an active ingredient can penetrate the skin.

Light aqueous formulations (serums, essences) penetrate faster but are less suitable for lipophilic active ingredients. Oil-in-water emulsions offer a good compromise for amphiphilic active ingredients. Water-in-oil formulations are suitable for very dry skin and form a more pronounced occlusion. Anhydrous formulations (pure oil formulations) provide optimal conditions for fat-soluble active ingredients such as vitamin E or phytosterols.

Penetration enhancers are substances that temporarily modify the skin's barrier function to increase active ingredient absorption. Established penetration enhancers include propylene glycol, dimethyl sulfoxide (DMSO, rare in cosmetics), oleic acid, and certain terpenes. They appear in the INCI list and can be an indicator of a formulation deliberately optimized for penetration.

Crucial is the compatibility between active ingredient and carrier substance: a hydrophilic active ingredient in a strongly hydrophobic carrier will be less bioavailable than in an aqueous system — and vice versa. A well-thought-out formulation systematically considers this compatibility.

Criterion 7 – Preservative System and Stability

Cosmetic formulations are microbiologically complex systems. Aqueous emulsions that contain nutrients for microorganisms must be effectively preserved — not only for regulatory reasons, but because microbial contamination compromises product safety and the integrity of active ingredients.

The debate surrounding preservatives in the cosmetic industry is complex. Parabens — the industry standard for decades — have been viewed with increasing criticism in recent years, although the EU's SCCS considers most parabens safe at approved concentrations. Phenoxyethanol is considered a well-tolerated alternative but is discussed in relation to sensitive skin and infant products. Preservatives like caprylyl glycol, benzyl alcohol, and ethylhexylglycerin are often used in combinations to achieve broader antimicrobial efficacy at lower individual concentrations.

Preservative-free systems are possible, but require constructive countermeasures: anhydrous formulations, airtight pump packaging without contamination risk, high alcohol content, or strongly acidic pH values that inherently inhibit microorganisms. Products marketed as "preservative-free" without communicating one of these alternative strategies should be critically assessed regarding their microbiological stability.

Criterion 8 – Light Protection Packaging and Product Integrity

The packaging of a skincare product is not just a marketing tool — it is part of the product protection system and significantly determines the stability of oxidation-sensitive active ingredients throughout the entire period of use.

Vitamin C (L-Ascorbic Acid) oxidizes measurably in clear glass bottles within a few days of light exposure. Retinol behaves similarly: UV-induced photoisomerization can significantly reduce biological activity. These chemical processes also occur under normal bathroom conditions — diffuse daylight is enough to destabilize sensitive formulations.

Effective packaging strategies include UV-absorbing or opaque containers (brown glass, opaque plastic), airtight pump systems that minimize contact between the product and ambient air, and airless technology, which prevents oxygen ingress through pressure equalization. Jars with wide openings, while convenient for dispensing, expose the product to air and germs with each opening — a structural disadvantage that high-quality formulations must compensate for with robust preservative systems or anhydrous formulations.

Therefore, examine not only the contents but also the packaging: Can light pass through the product? Does it have a pump dispenser or is it dispensed with a jar finger? Is there an airless system? These parameters are relevant for assessing the actual shelf life after opening.

Criterion 9 – Skin compatibility and dermatological testing

Efficacy and compatibility are not mutually exclusive properties — but they are in a state of tension that must be resolved through careful formulation and testing. A highly concentrated retinol serum can be clinically effective and at the same time cause irritation in a significant proportion of users if the formulation is not adequately buffered, stabilized, or balanced by supplementary emollient and soothing substances.

Dermatological tests in practice usually include the Repeated Open Application Test (ROAT), the Epicutaneous Patch Test, and clinical compatibility studies with standardized assessment tools for redness, irritation, dryness, and subjective comfort perception. The statement "dermatologically tested" on the packaging is not defined by regulations — it merely means that some form of dermatological testing has taken place, without specifying the methodology.

More meaningful are statements such as "tested on sensitive skin," "tested according to ISO 10993," or specific details on test methodology and number of subjects. For specific target groups — such as individuals with rosacea, atopic dermatitis, or post-procedural skin after aesthetic treatments — even stricter compatibility criteria are appropriate. A product recommended equally for all skin types, without making this differentiation, oversimplifies a complex physiological reality.

Your own tests remain indispensable: first apply new products to a small area of skin (inner forearm bend) for 24 to 48 hours before using them on your face. Even clinically well-documented products can trigger reactions in individuals with certain predispositions that were not represented in the study population.

How to apply the nine criteria in everyday life

Systematic application of these nine criteria does not require laboratory equipment. A structured checklist when purchasing products — INCI positioning of key active ingredients, communication of concentrations, pH indication, packaging type, study references — already allows for a significantly more informed purchasing decision than evaluating packaging design or marketing promises.

The most important transition is conceptual: from the question "How does this product feel?" to "Why should this product work?" Both questions are valid — but only the second distinguishes between a care experience and a demonstrably effective anti-aging formulation.