Note: this section discusses actives excluding ultraviolet filters, humectants, emollients, occlusives, and barrier lipids. These are assessed separately via their own analysis modules; see related articles.

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We classify an ingredient as an active if there is evidence demonstrating it targets a specific skin process or concern rather than contributing only to the product's structure, stability, sensory feel, or preservation. Some ingredients can have both active and functional roles. 

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However, just because an ingredient is classified as an active does not mean it is effective in addressing specific skincare concerns. Many so-called ‘actives’ have weak efficacy evidence, no reported effective concentration range in published peer-reviewed literature, and/or are not used in concentrations demonstrated to be effective in studies. In addition, formulation-specific factors such as the active delivery system and the product’s pH environment have a direct impact on the efficacy of the active. 

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What Aelon IQ analyses​​

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Presence at an effective concentration

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The amount of an active present in a formulation matters because an ingredient can only contribute a benefit if it is present at a concentration shown to produce a benefit. An ingredient list gives an indication of how much of each ingredient is present: ingredients are declared in descending order of the weight at which they are added, so those higher in the list are present in greater amounts, although below 1% they may be listed in any order (European Parliament and Council of the European Union, 2009). This allows an active's concentration to be estimated, but only approximately: the ordering gives a band rather than a figure.

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Once we estimate each ingredient's concentration, we then compare it with the minimum concentration at which that ingredient has been shown to work, where such data exists. Two problems affect the availability of minimum effective concentration data. First, cosmetics are not medicines, and the obligation is not that an ingredient's effective dose be proven, but that any claim a brand makes be substantiated (European Commission, 2013) — an obligation that can be met using claims language that requires a low evidence bar (e.g., 'visibly reduces the appearance of wrinkles' rather than 'reduces wrinkle depth by X%'). Where the supplier of the active or the manufacturer of the formulation has generated any evidence to substantiate claims, that evidence, including any data on effective concentration, typically sits in proprietary efficacy dossiers used to market the ingredient or the product by parties with strong commercial interest, and is generally neither peer-reviewed nor publicly available. 

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Second, where a figure can be found, its meaning varies. It may be a concentration shown to work in a controlled human trial, or it may be a typical use level — the concentration at which an ingredient is conventionally formulated, limited by texture, stability, cost, or legal restrictions. Effective concentrations are more frequently found for actives backed by higher levels of evidence (see the evidence hierarchy below), whereas typical use levels are most often used for actives for which only Level IV or V evidence exists. 

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We consider an active as contributing a likely benefit — qualified — only when its estimated concentration within the formulation reaches the lowest reference concentration we could find. Where the estimated concentration of the active falls below the minimum reference concentration, or where no usable reference concentration could be found, we do not credit the active with a beneficial effect. This is not a verdict that the active does absolutely nothing for the skin - models rely on incomplete information and estimates and assumptions which can be incorrect. Our verdict reflects our interpretation of available evidence, which is messy, patchy, often low quality, and frequently produced and promoted by parties with commercial incentives.   

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Strength of the evidence

 

Once we determine if the active is qualified, meaning it is present in the formulation in estimated concentrations that meet at least the lower efficacy concentration threshold, our model grades the level of available evidence supporting the use of the active, where Level I evidence provides the strongest support for the active's use. Note that our custom scale does not include systematic literature reviews and meta-analyses. A review or meta-analysis is only as reliable as the primary studies it pools, which for cosmetic actives are often few, of mixed quality, or not directly comparable. So rather than credit the review itself, we grade the strength of the primary study behind it.
 

• Level I: Double-blind randomised controlled trial (RCT) in humans (including double-blind split-face). 

• Level II: RCT that is not double-blind (single-blind, open-label, or blinding not reported).

• Level III: Controlled trial without randomisation (comparison group, not randomly assigned).

• Level IV: Human study with no control group (single-arm, case series).

• Level V: Preclinical or mechanistic evidence of a specific bioactive mechanism relevant to a skin process or concern: animal models, ex-vivo human skin, in-vitro cell/tissue culture (human or animal), a cell-free biochemical or enzyme assay; proprietary manufacturer/supplier efficacy dossiers.

 

Mechanism of action

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Mechanism is assessed in two respects: the type of mechanism through which an active acts (since mechanism types differ in the magnitude of effect they produce in the skin) and whether it complements the mechanisms of the other actives present. The processes underlying visible ageing are not independent of one another. Oxidation and inflammatory signalling, for instance, reinforce each other and together drive degradation of the matrix proteins that give skin its firmness (Nan, L., et al., 2025). Where a formulation's actives attempt to address such processes synergistically, the assessment credits it.

 

The basis for this synergy credit is generally mechanistic rather than clinical: combinations of cosmetic actives are seldom tested against their individual components in controlled trials. It reflects the coherence of the underlying biology, not a demonstrated margin over a single-active formulation.

 

Delivery to the site of action

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An active present in sufficient quantity, and supported by even the highest level of evidence, must still reach the layer of skin in which it acts. The stratum corneum is a barrier: some molecules cross it readily; others depend on the formulation to carry them. Some actives are stability-sensitive and require encapsulation to shield them from breaking down before they reach the skin. Other actives work better released gradually rather than all at once. Some actives need a solubilising system to remain dispersed in the product and evenly distributed across the skin. Yet others need assistance crossing the barrier itself. The form in which an ingredient is delivered, not merely its presence in the formulation, governs how much of it reaches the layer where it acts. Where an active requires none of this support, delivery is not assessed for it.

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A compatible formulation pH

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Many actives only work within a particular pH window – too far outside it and the active doesn't perform as intended or breaks down before it can act. Vitamin C is the familiar example: it must be formulated in quite a narrow, distinctly acidic range in order to be effective.

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So the assessment, applied to water-based products (waterless products have no meaningful pH) asks two things. First, does the product's likely pH fall where the active actually works? Second, is that pH built to last? A formula can be mixed to the right pH but have nothing to hold it there, drifting out of range, while a more robustly built one stays put. An active is served well only when both are true — the right pH, and a formula that maintains it.

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Ratio of qualifying to disqualified actives

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This assessment scores the ratio of actives likely to be effective based on the above 5 criteria (qualified actives) vs those that are not (disqualified), showing how much of the INCI list reflects potentially beneficial activity.

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Summary

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These factors explain why a long list of actives on a label tells you little about how effective a product is likely to be. An active is more likely to be effective when it has published effective concentration data and meets that threshold in the formulation; the evidence supporting its use is robust; it works through a high-impact biological mechanism and synergistically with other actives; the formulation delivers it to where it works, and (in water-based products) the pH permits activity and remains stable.

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References 

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European Parliament and Council of the European Union (2009) Regulation (EC) No 1223/2009 of the European Parliament and of the Council of 30 November 2009 on cosmetic products. Official Journal of the European Union, L 342, 22.12.2009, pp. 59–209.

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European Commission (2013) Commission Regulation (EU) No 655/2013 of 10 July 2013 laying down common criteria for the justification of claims used in relation to cosmetic products. Official Journal of the European Union, L 190, 11.7.2013, pp. 31–34.

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Nan, L., Guo, P., Hui, W., Xia, F. and Yi, C. (2025) 'Recent advances in dermal fibroblast senescence and skin aging: unravelling mechanisms and pioneering therapeutic strategies', Frontiers in Pharmacology, 16, 1592596. doi:10.3389/fphar.2025.1592596.​​​