RHPE Model: Mapping Pigmentary Changes in Atopic Dermatitis

Beyond the itch: Atopic dermatitis and pigmentary disorders 

Atopic dermatitis (AD) is the most common chronic inflammatory skin disorder affecting up to 25% of children and 10% of adults worldwide. AD is a complex and multifactorial disease with a significant impact on the quality of life of people who suffer from it.

AD is characterized by profound barrier dysfunction and immune dysregulation. Beyond the hallmark pruritus and xerosis, AD frequently precipitates secondary pigmentary disorders that significantly impact the visual and psychological health of the patient.

Atopic dermatitis (AD) is traditionally defined by a T-helper 2 (Th2) cell-mediated immune response that compromises the integrity of the stratum corneum with IL-4, IL-13, and IL-31 as key cytokines mediating disease initiation and progression. However, modern dermocosmetic science recognizes that the types of eczema encountered in clinical practice are increasingly defined by their long-term visual sequelae. In people with darker skin tones (higher Fitzpatrick phototypes), the inflammatory cascade of the immune system does not merely resolve; it leaves behind a landscape of inflammatory hypopigmentation or hyperpigmentation. Understanding this skin condition requires moving beyond the surface-level itch to address the underlying cellular memory that dictates skin tone uniformity. 

The unseen connection: Linking atopic dermatitis and pigmentary changes 

The clinical correlation between AD and pigmentary shifts is most evident in the manifestation of pityriasis alba (PA). PA is characterized by ill-defined, scaly, hypopigmented macules that often appear on the face and forearms of children. While historically dismissed as a minor cosmetic concern, research now confirms that PA is a direct functional consequence of the chronic inflammation associated with atopic skin, leading to a localized dropout of visible melanin, negatively impacting self-esteem and quality of life.

The invisible barrier: Why is studying pigmentary alterations in dermatitis so complex? 

Scientific investigation into hyperpigmentation has been historically hindered by the lack of high-fidelity models. Despite its prevalence, the mechanisms linking chronic inflammation and skin pigmentation alterations in AD remain poorly understood, partly because existing AD models focus almost exclusively on keratinocytes and fibroblasts. Traditional 2D cell cultures fail to simulate the three-dimensional crosstalk between keratinocytes and melanocytes, while animal models do not accurately replicate the human pigmented epidermis. This has left a significant knowledge gap in the R&D of active ingredients specifically designed to stabilize pigment during an inflammatory flare. 

What is the reconstructed human pigmented epidermis (RHPE) model? 

The RHPE model is a sophisticated 3D in vitro platform that recreates the stratified human epidermis by integrating functional melanocytes into a keratinocyte-based scaffold. It allows for the study of melanosome transfer, skin pigmentation and barrier improvement in a human-relevant environment. 

The development of the Reconstructed Human Pigmented Epidermis (RHPE) model represents a paradigm shift in dermocosmetic research. Unlike standard 3D epidermal models, RHPE incorporates primary human melanocytes, typically at a ratio that mimics human physiology (approximately 1:20 melanocytes to keratinocytes). This architecture enables researchers to observe and investigate the interaction between melanocytes located in the basal layer and keratinocytes in that layer and in upper strata, providing a mechanistically informative platform for testing bio-active naturals. 

A technical overview of the RHPE and RHPE-AD models 

The RHPE model is constructed through the air-liquid interface (ALI) culture technique, which promotes the differentiation of keratinocytes into a fully cornified stratum corneum. This process ensures that the barrier function of the model is well established.  Furthermore, by the application of topical inflammatory triggers, such as an atopic mix of cytokines (e.g., IL-4, IL-13, IL-31a), it is possible to simulate the AD phenotype in vitro and study the associated barrier dysfunction (Bajsert et al., 2025). 

The game changer: Combining RHE and melanocytes to simulate pigmentary changes in an AD skin model

By integrating melanocytes into the basal layer, the RHPE model allows for direct quantification of melanogenesis and pigment transfer from melanocytes to keratinocytes. In a healthy state, melanocytes extend their dendrites to transfer melanin to surrounding keratinocytes. The RHPE-AD variant is, to our knowledge, the first model to specifically reproduce the hypopigmented pattern characteristic of PA—that is, the impairment of pigmentation in the inflammatory context of AD. This highly innovative model will allow researchers to test the efficacy of various candidate ingredients for improving skin tone in inflammatory conditions (Bajsert et al., 2025). 

Why it matters: Advantages of using RHPE for dermatological research 

The primary advantage of the RHPE model lies in its ability to provide human-relevant data without the ethical and regulatory hurdles of animal testing. It offers high reproducibility for screening active ingredients and allows for the isolation of specific molecular pathways—such as the NRF2 antioxidant pathway—that are often obscured in whole-organism clinical trials. 

Key findings from the RHPE-AD model study 

Recent studies by Provital and Universitat Autònoma de Barcelona utilizing the RHPE-AD model have identified a systematic downregulation of melanogenesis-related genes and a concomitant loss of structural proteins. These findings provide a molecular blueprint for the development of targeted atopic skincare. 

In a landmark study, the RHPE model was exposed to an inflammatory cytokine cocktail to simulate Atopic Dermatitis (RHPE-AD). The results revealed a significant atopic phenotype characterized by increased inflammation markers and a parallel decrease in both barrier and pigmentary markers. Specifically, gene expression analysis by RT-qPCR showed an upregulation of Carbonic Anhydrase 2 (CA2) and Interleukin-23 (IL23p19), interleukin 1 (IL1α) and interleukin 6 (IL6), key biomarkers associated with AD and severe epidermal distress (Bajsert et al., 2025). 

Visualizing the damage: Pigmentary disruptions in atopic dermatitis and pityriasis alba 

Advanced imaging of the RHPE-AD model demonstrated a clear visual reduction in pigment intensity, which correlated with the progressive decrease in melanin content analyzed by image quantification over time. Our findings reveal, for the first time to our knowledge, that the RHPE-AD is an in vitro model that replicates at the macroscopic level the white patches of pityriasis alba seen in clinical settings (Alexis et al., 2025; Nguyen et al., 2024; Gan et al., 2023). Furthermore, the study confirmed that the hypopigmentation is not due to a total loss of melanocytes, but rather a profound disruption in how pigment is produced and transported within the tissue.

Under the microscope: Inflammatory and structural alterations in RHPE-AD 

Histological analysis of the RHPE-AD model identified spongiosis—intercellular edema—within the basal layer. This structural weakening is accompanied by a thinning of the granular layers and a loss of cohesion between cells. This data confirms that you cannot fix the tone without repairing the biological components of the epidermis. 

The genetic blueprint: Molecular and gene expression insights from RHPE-AD 

To better understand the mechanisms underlying the effects of AD-like cytokine cocktail on the RHPE model, we conducted an RT-qPCR analysis of genes relevant to barrier function as well as an immunofluorescence to visualize and analyze the expression of key epidermal proteins involved in epidermal differentiation and barrier function of human epidermis. The study highlighted a dramatic reduction in essential barrier proteins: Filaggrin (FLG), Loricrin (LOR), and Involucrin (IVL), demonstrating that the RHPE-AD model replicates the barrier function disruption associated with this skin inflammatory disorder.

Simultaneously, key melanogenesis genes, including MITF (Microphthalmia-associated transcription factor), PMEL, and DCT, were significantly downregulated, suggesting a pigmentary dysfunction. This dual failure explains why atopic skin is simultaneously fragile and prone to uneven tone (Bajsert et al., 2025). 

The inflammaging effect: The role of inflammation in pigmentary disorders 

Chronic inflammation acts as a biological deregulator of melanogenesis. Pro-inflammatory cytokines like IL-6 and IL-1a suppress the signaling pathways required for healthy pigment production and distribution (B Swope et al., 1991). 

Chronic inflammation can impair melanogenesis through the action of pro-inflammatory cytokines such as IL-6 and IL-1, which have been shown to suppress melanogenic signaling pathways and reduce tyrosinase activity in melanocytes (meter ref). However, the effects of inflammation on skin pigmentation are context-dependent and may contribute to either hypo- or hyperpigmentation.

The cytokine storm: How inflammatory cytokines direct pigmentation 

Inflammation is the primary driver of pigmentary shift in AD. High concentrations of IL-1a and IL-6 exert an inhibitory effect on the MITF pathway. In the RHPE-AD model, these cytokines act as “signal blockers,” preventing the melanocyte from receiving the cues necessary to synthesize melanin. This results in what is termed inflammatory hypopigmentation, where the skin loses its ability to maintain its natural hue. 

Disrupted melanin distribution in atopic skin 

Even when melanin is synthesized, its distribution is compromised. The RHPE-AD study revealed a microscopic “traffic jam” where melanosomes are produced but fail to reach the upper keratinocytes. This disruption in melanin transfer and the subsequent alteration of melanin distribution throughout the various layers of keratinocytes leads to a patchy, dull appearance that lacks the uniform radiance associated with healthy skin. 

Formulating for success: Implications for dermocosmetic treatments 

These findings suggest that traditional skin-brightening agents (like Hydroquinone or high-dose Vitamin C) may be too aggressive for atopic skin. Instead, the industry is shifting toward bio-active naturals that focus on signal correction—restoring the balance between the immune system and the melanocyte without inducing further irritation. 

Uncovering the mechanics: Why pigmentation changes in atopic dermatitis and pityriasis alba 

Our studies with the RHPE-AD model suggest that pityriasis alba is driven by melanin clustering and a reduction in melanocyte dendricity. These ultrastructural changes prevent the even spread of melanin across the skin surface (Bajsert et al., 2025). 

The cluster effect: Melanin aggregation and keratinocyte dysfunction 

Transmission Electron Microscopy (TEM) analysis of the RHPE-AD model uncovered a startling phenomenon: melanin clustering. Rather than being distributed evenly as a protective cap over the keratinocyte nucleus, the melanin was found in dense, irregular aggregates. This clustering prevents the pigment from effectively concealing skin’s color, contributing to the faded look of PA lesions (Bajsert et al., 2025). 

Retracted reach: Altered melanocyte function and reduced dendricity 

A critical finding in the RHPE-AD research was the observation of reduced melanocyte dendricity. Under inflammatory stress, melanocytes retract their dendritic “arms”. Since these “arms” are the physical conduits for pigment delivery, their retraction disrupts the melanin transfer to the surrounding 30-40 keratinocytes that each melanocyte typically serves (Bajsert et al., 2025). 

Gene expression and oxidative stress in RHPE-AD 

The study also noted a significant depletion of antioxidant markers, specifically NRF2 and SOD1 (Superoxide Dismutase 1). This indicates that atopic skin is in a state of chronic oxidative stress, which further damages the melanocyte’s delicate machinery. Formulations must therefore include efficacious, concentrated antioxidants to stabilize the cellular environment (Bajsert et al., 2025). 

Shaping the future: The impact of RHPE on dermocosmetic research and innovation 

RHPE models empower R&D departments to develop precision natural ingredients that address both barrier repair and pigmentary stability. This represents the next frontier in ethical, high-performance skincare. 

Ethical excellence: Non-Animal testing and human-relevant models 

As global regulations (such as the EU Cosmetics Regulation) strictly prohibit animal testing, the RHPE model offers a compliant, scientifically superior alternative. It allows for the validation of claims regarding skin tone uniformity in a way that is both ethical and high efficacious.

Advancing active ingredient development for improved pigmentation and barrier function

The RHPE-AD model serves as a high-throughput screening tool for the next generation of bio-active naturals. By monitoring the recovery of the expression of specific genes in the model related to pigmentation or barrier function, such as MITF and FLG respectively, researchers can identify ingredients that truly re-synchronize the skin’s biological functions (Bajsert et al., 2025). 

The new frontier: Targeting post-inflammatory pigmentation in dermocosmetic solutions 

The future of the industry lies in products that pursue total epidermal restoration. The RHPE-AD model serves now as a platform to develop new active ingredients that could reverse melanin clustering. This allows brands to offer consumers targeted solutions that address the specific, underlying causes of atopic pigmentary disorders. 

The future of atopic dermatitis and pityriasis alba research with RHPE-AD models 

The RHPE-AD model has transformed our understanding of how inflammation sabotages skin tone. It provides a roadmap for future R&D to focus on melanocyte’s dendritic health, melanin distribution in keratinocytes, antioxidant restoration, and structural barrier repair. 

A new era of understanding: Advancements in inflammation and pigmentation 

The integration of melanocytes into 3D skin models has revealed that atopic pigmentation is a structural and genetic dysregulation, rather than a mere surface manifestation. The ultrastructural insights gained from the RHPE-AD study—particularly regarding melanin clustering —will remain the gold standard for atopic research for the next decade. 

The power of nature: Potential for new treatments and active ingredients in skincare 

The complexity of atopic skin requires a sophisticated approach. Bio-active naturals that can modulate multiple pathways simultaneously—barrier repair, antioxidant defense, and pigmentary function—are the most efficacious tools at our disposal. As we continue to refine the RHPE-AD model, the bridge between nature and 3D skin engineering will only grow stronger, leading to a new generation of inclusive, high-performance skincare. 

Key takeaways 

• The model: RHPE-AD is the first 3D skin model to successfully replicate both the inflammatory and pigmentary alterations of Atopic Dermatitis and Pityriasis Alba (Bajsert et al., 2025). 
• Ultrastructural discovery: Hypopigmentation in AD is driven by an abnormal distribution of pigment in keratinocytes in the form of melanin clusters and a reduced melanocyte dendricity, not just a lack of melanin production. 
• Molecular targets: Formulations should aim to downregulate CA2 and IL-6, IL1α and IL23p19, while upregulating FLG, LOR, IVL, K10 and MITF. 
• Oxidative defense: Restoring NRF2 and SOD1 levels is essential to protect melanocytes from inflammatory-induced retraction. 
• The natural advantage: High-activity botanical extracts are uniquely suited to the multi-pathway modulation required to restore atopic skin uniformity. 

For further information or insights on this topic, please do not hesitate to contact our team of experts, who are available to provide guidance and support in selecting the most suitable solutions for your requirements.