Uneven skin tone and dark spots associated with melasma, post-inflammatory hyperpigmentation, and photo-induced lentigines are among the most persistent cosmetic concerns worldwide. An international expert consensus indicates that visible pigmentation outcomes are determined by multiple interacting factors beyond melanocyte activity alone, including lesion depth, inflammatory history, ultraviolet and visible light exposure, hormonal influences, dietary factors (1), (2) such as vitamins C, B12, D, and B3, iron, and tyrosine, as well as relapse dynamics (3).

Broad-spectrum UV filters reduce hyperpigmentation primarily by limiting UV- and visible-light–induced melanogenic stimulation, oxidative stress, and inflammation. Consistent use of high SPF and strong UVA protection decreases the incidence and severity of melasma and post-inflammatory hyperpigmentation, while visible-light attenuation, notably with iron oxides, further improves protection in higher Fitzpatrick phototypes. However, UV filters do not actively reverse established pigmentation and remain highly dependent on correct, sustained application; moreover, UV protection alone is often insufficient to prevent relapse in chronic pigmentary disorders such as melasma, highlighting the need for adjunctive pigment-modulating cosmetic actives (3).

This multifactorial nature explains why topical cosmetic approaches often yield gradual, partial, or unstable improvement, particularly in higher Fitzpatrick phototypes where inflammation-induced pigmentation and relapse risk are elevated (1). From a cosmetic R&D perspective, these constraints narrow the efficacy–tolerability window: actives intended for daily, long-term use must deliver visible benefit without provoking irritation or barrier disruption that could counteract tone-evening effects.

Melanin synthesis within melanocytes is a multistep and tightly regulated process. Tyrosinase (TYR) functions as the rate-limiting enzyme, supported by tyrosinase-related proteins TRP-1 and TRP-2. Their coordinated expression is largely governed by microphthalmia-associated transcription factor (MITF), which integrates signals from ultraviolet radiation, oxidative stress, inflammatory mediators, and paracrine factors released by keratinocytes and fibroblasts (3), (4), (5).

Hyperpigmented skin consistently exhibits elevated expression of TYR, and TRP-1 compared with adjacent normal skin (3), (4). This supports the view that visible dyschromia reflects sustained pathway upregulation rather than isolated enzymatic hyperactivity. Consequently, modulation of melanogenic enzyme expression represents one mechanism by which melanin output may be gradually reduced while preserving basal pigmentation and melanocyte viability.

Tyrosinase inhibitors are widely used in cosmetic formulations to reduce melanin synthesis by blocking the rate-limiting step in melanogenesis, which can improve the appearance of epidermal hyperpigmentation over weeks of consistent use. Their efficacy varies with chemical structure, skin phototype, and lesion type, and clinical improvements are often moderate rather than complete. Common examples such as α-arbutin and kojic acid demonstrate measurable inhibition of tyrosinase activity with generally tolerable safety profiles at regulated usage levels, but potent inhibitors may cause irritation or cytotoxicity, and some traditional agents have been restricted due to safety concerns. Tyrosinase inhibition alone does not fully address upstream melanogenic signalling, melanosome transfer, or external triggers like UV exposure, contributing to partial responses and frequent relapse in hyperpigmentation management. Sources for these points include comprehensive reviews of tyrosinase inhibitors and their mechanisms, structure-activity relationships, and safety considerations in cosmetic use (5), (6), (7).

Visible pigmentation is determined not only by the amount of melanin produced, but also by how efficiently melanosomes are transferred from melanocytes to keratinocytes and distributed within the epidermis. Multiple transfer mechanisms have been described, including keratinocyte-mediated phagocytic uptake regulated by receptors such as protease-activated receptor-2, as well as cytophagocytosis and membrane-mediated transfer (8), (9).

These processes are influenced by inflammatory signaling and the cutaneous microenvironment, reinforcing the concept that pigmentation is regulated at the tissue level rather than by melanocytes alone (3), (9). Clinical consensus increasingly recognizes epidermal–dermal interactions and inflammatory cues as key drivers of persistence and relapse in visible hyperpigmentation (1).

Synthesizing current biological understanding and clinical guidance, next-generation cosmetic depigmenting actives may be defined by the following criteria:

1. Regulatory modulation of melanogenesis, emphasizing controlled downregulation of melanogenic enzyme expression alongside or in complement to catalytic inhibition (8), (9).
2. Integration of downstream processes, including melanosome transfer and epidermal handling of pigment (10), (11).
3. Objective efficacy assessment, using interpretable endpoints such as Individual Typology Angle (ITA), ΔE, and standardized imaging (12).
4. High tolerability for long-term use, minimizing irritation-mediated relapse risk, particularly in higher phototypes (1).
5. Compatibility with photoprotection strategies, acknowledging that topical actives cannot compensate for insufficient ultraviolet and visible-light protection (2), (13).
6. Low effective use levels, supporting formulation flexibility and favorable safety margins.

This framework does not exclude established depigmenting mechanisms but situates them within a broader, tissue-level understanding of visible pigmentation.

Meaningful cosmetic improvement should be detectable within 8–12 weeks using objective and reproducible tools, while supporting maintenance beyond the initial response period (1). Colorimetric parameters such as ITA, derived from L* and b* values, provide a quantitative bridge between instrumental change and perceived skin tone when measured under controlled conditions (8). Standardized photography complements these measurements by contextualizing reductions in spot contrast and overall tone heterogeneity.

In real-world practice, multiple complementary techniques contribute to the management of visible hyperpigmentation. These include procedural approaches such as chemical peels and energy-based devices, optical strategies including tinted photoprotection and corrective makeup, and formulation-driven methods that enhance light scattering or color correction (2), (13). Nevertheless, topical depigmenting actives remain central because they are compatible with daily, long-term use and can be integrated into maintenance regimens alongside photoprotection.

Within this evolving framework, recent experimental programs have explored molecule classes designed to downregulate melanogenic enzyme expression while also influencing melanosome transfer pathways, rather than acting as direct tyrosinase inhibitors (8), (9), (13).

One illustrative example is Glucuronyl Glucosyl Oleanolate (Tonasulike-D), a glucuronylated triterpenoid derivative introduced to the market in 2025 by Kokuma. Experimental data describing its effects on melanogenic enzyme expression and markers associated with melanosome transfer have been presented as a scientific poster at the IFSCC Congress 2025. These results, generated in cellular and ex vivo models, suggest that coordinated modulation of pigmentation-related pathways at low use levels without direct inhibition of human tyrosinase catalytic activity can deliver strong efficacy. Tonasulike-D further validated this approach by delivering excellent results during in vivo trials. As such, this example illustrates this multi-level approach, while remaining distinct from historical tyrosinase inhibitors.

Future progress in cosmetic depigmentation is unlikely to be driven solely by stronger suppression of a single enzymatic target. Instead, advances will depend on reframing visible pigmentation as a regulated, tissue-level process and developing actives that rebalance melanogenic enzyme regulation, melanosome transfer, and microenvironmental signaling within cosmetic safety and regulatory boundaries (2-9), (10), (11). By integrating established mechanisms with emerging regulatory strategies, next-generation depigmenting actives may expand the options available to formulators seeking durable, inclusive, and tolerability-aligned tone-evening solutions.