Efficacy of a Multi-lamellar Emulsion Containing a Synthetic Sphingosine Kinase 1 Activator and Pseudoceramide in Patients with Atopic Dermatitis: A Randomized Controlled Trial.

INTRODUCTION: Patients with atopic dermatitis (AD) have impaired barrier function, which decreases skin hydration, weakens their defense against microorganisms, and culminates in increased inflammatory responses. Here, we conducted a clinical trial to evaluate the efficacy of a multi-lamellar emulsion (MLE) containing the pseudoceramide PC-9S and a synthetic sphingosine kinase 1 (SPHK1) activator, Defensamide™, in improving mild-to-moderate atopic dermatitis. METHODS: Forty patients aged ≥ 2 years were randomized into a combined-therapy group treated with the MLE containing PC-9S and Defensamide™ plus a topical corticosteroid and a topical-corticosteroid-only group. Assessments based on therapeutic methods included the Eczema Area and Severity Index (EASI), the Investigator Global Assessment (IGA), transepidermal water loss (TEWL), stratum corneum hydration (SCH), skin dryness, a visual analogue scale (VAS) of itchiness, a VAS of sleep disturbance, patient satisfaction, and the Dermatology Life Quality Index (DLQI). RESULTS: Thirty-eight patients completed this study. In the combined-therapy group, significant improvements in clinical and instrumental measures such as EASI scores, skin hydration, and skin dryness were noted at 4 weeks compared to baseline, but such improvements were not noted in the topical corticosteroid-only group. Subjective assessments of itching and sleep disturbance and DLQI scores also showed significant improvements in the combined-therapy group. CONCLUSION: Combined therapy with the MLE containing Defensamide™ and PC-9S and with topical corticosteroid demonstrated superior clinical outcomes compared with topical corticosteroid monotherapy. Our findings underscore the potential of MLE-containing formulations as effective adjunctive therapies for AD, offering both objective and subjective symptomatic relief and enhancing patients' quality of life.

The Role of Genetics on Psoriasis Susceptibility, Comorbidities, and Treatment Response.

This review highlights advances made in psoriasis genetics, including findings from genome-wide association studies, exome-sequencing studies, and copy number variant studies. The impact of genetic variants on various comorbidities and therapeutic responses is discussed.

Vitamin D supplementation can enhance therapeutic effects of excimer laser in patients with vitiligo.

PURPOSE: Vitiligo is a disease of acquired depigmentation characterized by the destruction of melanocytes. A theoretical association between low level of 25-hydroxyvitamin D [25(OH)D] and vitiligo has been previously suggested. The objective of this study was to determine the efficacy of intramuscular injection of cholecalciferol with excimer laser compared with the excimer laser alone for vitiligo treatment. METHODS: This study included 26 patients diagnosed with non-segmental vitiligo and low serum 25(OH)D levels (<20 ng/mL). The participants were randomly divided into two groups through randomization. The treatment using a 308-nm excimer laser was administered to both groups, and the study group additionally received cholecalciferol injection. RESULTS: The Vitiligo Area Scoring Index (VASI) scores showed an 83.6% improvement over the initial score in the study group, whereas the control group showed a 54.7% improvement after 6 months of treatment. After 6 months of treatment, the study group showed a significantly higher proportion of patients who achieved VASI50 and VASI75 compared with the control group. CONCLUSION: Intramuscular injection of cholecalciferol can be a supplemental option for the treatment of vitiligo patients with vitamin D deficiency with excimer laser therapy.

Case Report: Erythema Multiforme Induced by Lithium Contact.

Erythema multiforme (EM) is an acute, self-limited mucocutaneous disease with diverse triggering factors, and the recurrences are quite common. A 24-year old male presented with multiple erythematous, itchy papules and plaques on multiple sites. He has worked in a lithium battery factory and experienced the chemical burn 2 weeks ago. A histopathologic examination on right wrist showed a scattered lymphocytic infiltration, vacuolar degeneration, and necrotic keratinocyte. The final diagnosis was EM after occupational lithium exposure. He was treated by oral methylprednisolone and experienced recurrences after returning to the same workplace after remission. Although the precise pathogenesis is unknown, the pathogenesis of EM by lithium is related to the effect of lithium on immune system, different from other etiologies. To our knowledge, our case is the first report of EM following the chemical burn and occupational lithium exposure. We report this as an interesting case of EM.

Multiple Eruptive Epithelioid Hemangiomas on the Right Upper Extremity in an Asian Man.

Epithelioid hemangioma is a rare benign vascular neoplasm. Recently, the term "multiple eruptive epithelioid hemangioma" has been proposed for epithelioid hemangioma with distinct features. It is different from usual epithelioid hemangioma because of the multifocal distributions in various body regions with an eruptive onset. In addition, the histopathology of multiple eruptive epithelioid hemangioma shows increased cellular proliferation, mitosis, and nuclear pleomorphism and positive findings for FOS-B compared to classic epithelioid hemangioma. Herein, we report the case of a 59-year-old man with unusual manifestations suitable for multiple eruptive epithelioid hemangioma. He had multiple erythematous to purple-red dome-shaped nodules on the right hand, arm, and shoulder. The initial lesion was a solitary erythematous nodule on the right hand that abruptly extended to the right arm and shoulder. Microscopically, the tumor was a well-demarcated dermal nodule and showed capillary sized vascular structures. Vascular structures had epithelioid endothelial cells with abundant eosinophilic cytoplasm and vesicular nuclei. The tumor cells showed mild nuclear pleomorphism and a few mitosis and feature of resembling cobble stone was observed. In immunohistochemistry, CD31 and CD34 were positive in the endothelial cells. The endothelial cells showed nuclear positivity in FOS-B. Based on the clinical and histopathological findings, the final diagnosis was multiple eruptive epithelioid hemangiomas. This is the first report of multiple eruptive epithelioid hemangiomas in an Asian man after the term had been introduced.

Adipose-Derived Stem Cell Exosomes Alleviate Psoriasis Serum Exosomes-Induced Inflammation by Regulating Autophagy and Redox Status in Keratinocytes.

Introduction: Exosomes play a key role in cell communication and are involved in both pathological and physiological processes. Autophagy dysfunction and oxidative stress are linked to immune-mediated inflammatory diseases such as psoriasis. Stem cell-derived exosomes exhibit immunomodulatory and antioxidant efficacy. Methods: We aimed to investigate the impact of psoriasis serum-derived exosomes on inflammation, oxidative stress, and autophagy in keratinocytes. Additionally, we explored the therapeutic potential of adipose-derived stem cell (ADSC) exosomes against inflammation induced by psoriasis serum exosomes. To validate psoriasis patient serum-derived exosomes and ADSC exosomes, we used nanoparticle tracking analysis, Western blotting, flow cytometry, and immunofluorescence. qPCR was used to study changes in the gene expression of proinflammatory cytokines and oxidative stress markers in HaCaT cells treated with psoriasis serum-derived exosomes or ADSC exosomes. The effects of these exosomes on autophagy in HaCaT cells were evaluated by Western blotting and immunofluorescence. Result: The treatment of HaCaT cells with psoriasis serum-derived exosomes increased proinflammatory cytokine production and oxidative stress-related factor (Nox2 and Nox4) expression and decreased Nrf2 expression via P65/NF-κB and P38/MAPK activation. Compared with healthy control serum-derived exosomes, psoriasis serum-derived exosomes decreased ATG5, P62, Beclin1, and LC3 expression and autophagosome production in HaCaT cells. Conversely, ADSC exosomes suppressed proinflammatory cytokine and oxidative stress production, and restored autophagy in HaCaT cells treated with psoriasis serum-derived exosomes. Discussion: These findings suggest that ADSC exosomes exhibit a suppressive effect on psoriasis serum exosome-induced inflammation and oxidative stress by regulating autophagy in keratinocytes.

Efficacy, Safety, and Subject Satisfaction of PrabotulinumtoxinA for Moderate-to-Severe Crow's Feet: A Phase IV, Multicenter, Double-Blind, Randomized, Placebo-Controlled Trial.

PrabotulinumtoxinA has been identified as an effective agent against crow's feet. Our study, which included Korean patients with moderate to severe crow's feet, was undertaken to compare the efficacy and safety of PrabotulinumtoxinA and placebo treatments. Of the 90 study participants, 60 received prabotulinumtoxinA (24 U), whereas 30 received a placebo. The primary outcome assessment included facial wrinkle grading by investigators. At week 4, 69.64% of patients in the prabotulinumtoxinA group exhibited minimal crow's feet severity; in contrast, a 0% improvement was observed in the placebo group (p < 0.0001). At week 12, the improvement rates were 30.36% for prabotulinumtoxinA and 6.90% for the placebo, demonstrating a significant difference (p = 0.0152). Based on the independent review panel's assessment at week 4, the improvement rate was 39.29% in the prabotulinumtoxinA group and 3.45% in the placebo group during maximum smiling. Additionally, patient satisfaction was notably higher in the prabotulinumtoxinA group (32.14%) than in the placebo group (10.34%) at week 4 (p = 0.0289). Both treatments displayed comparable safety profiles, with only mild local reactions reported as ADRs for one patient from the prabotulinumtoxinA group. Thus, prabotulinumtoxinA demonstrates significant potential as a potent and safe remedy for crow's feet.

Rapid Remission of Sunburn-Induced Guttate Psoriasis with Guselkumab.

Guselkumab is an anti-interleukin-23 monoclonal antibody that is approved for plaque psoriasis and psoriatic arthritis. We present a case of a 28-year-old female patient with acute onset of guttate psoriasis after a blistering sunburn. She had no personal or family history of psoriasis or chronic inflammatory skin disease. The guttate psoriasis was refractory to topical treatment. After the first dose of guselkumab (100 mg subcutaneous injection), the patient experienced near-clearance of her guttate psoriasis, with continued improvement and drug-free remission 8 months after cessation of treatment. Dermatologists could consider guselkumab as a treatment option for patients with guttate psoriasis. Future studies should examine the potential for guselkumab to induce drug-free remissions in guttate psoriasis.

Pigmented contact dermatitis and hair dyes: A retrospective case-control multicentre study in Korea.

BACKGROUND: Pigmented contact dermatitis (PCD), a rare variant of non-eczematous contact dermatitis, is clinically characterized by sudden-onset brown or grey pigmentation on the face and neck. It is hypothesized to be caused by repeated contact with low levels of allergens. OBJECTIVES: This study evaluated the risk of using hair dyes in patients with PCD in Korea. METHODS: A total of 1033 PCD patients and 1366 controls from 31 university hospitals were retrospectively recruited. We collected and analysed the data from the patient group, diagnosed through typical clinical findings of PCD and the control group, which comprised age/sex-matched patients who visited the participating hospitals with pre-existing skin diseases other than current allergic disease or PCD. RESULTS: Melasma and photosensitivity were significantly more common in the control group, and a history of contact dermatitis was more common in the PCD group. There were significantly more Fitzpatrick skin type V participants in the PCD group than in the control group. There was no significant difference in sunscreen use between the groups. Using dermatologic medical history, Fitzpatrick skin type and sunscreen use as covariates, we showed that hair dye use carried a higher PCD risk (odds ratio [OR] before adjustment: 2.06, confidence interval [CI]: 1.60-2.65; OR after adjustment: 2.74, CI: 1.88-4.00). Moreover, henna users had a higher risk of PCD (OR before adjustment: 5.51, CI: 4.07-7.47; OR after adjustment: 7.02, CI: 4.59-10.74), indicating a significant increase in the risk of PCD with henna dye use. Contact dermatitis history was more prevalent in henna users than in those using other hair dyes in the PCD group (17.23% vs. 11.55%). CONCLUSION: Hair dye use is a risk factor for PCD. The risk significantly increased when henna hair dye was used by those with a history of contact dermatitis.

Can we predict postinflammatory hyperpigmentation after laser treatment based on dermoscopic findings of solar lentigo?

Solar lentigo (SL) commonly occurs as hyperpigmented macules in areas exposed to ultraviolet radiation. It typically shows an increased number of melanocytes in the basal cell layer of the skin, with or without elongated rete ridges. This retrospective study aimed to evaluate the characteristic dermoscopic patterns, reflecting different histopathological features, which might be valuable in predicting the possibility of postinflammatory hyperpigmentation (PIH) occurring after laser treatment. In total, 88 Korean patients diagnosed with biopsy-proven SL (a total of 90 lesions were diagnosed) between January, 2016 and December, 2021 were included. Histopathological patterns were classified into six categories. Dermoscopic features were classified into six categories. Pseudonetwork pattern and rete ridge elongation showed a statistically significant negative correlation. This means that a flatter epidermis is likely to manifest as a pseudonetwork pattern. The erythema pattern showed a significant positive correlation with interface changes and inflammatory infiltration. Bluish-gray granules (peppering), a characteristic dermoscopic finding, showed significant positive correlations with interface changes, inflammatory infiltration, and dermal melanophages. Clinicians considering laser treatment for patients with SL should perform dermoscopic tests before treatment. The pseudonetwork relates to flattened epidermis and fewer Langerhans cells; thus, a lower remission of PIH after laser treatment might be expected. If bluish-gray granules or erythema are observed, inflammatory conditions are likely to be involved. In such cases, regression of the inflammatory response through drug therapy, such as topical corticosteroids, should be a priority option before laser treatment.

Pathogenesis and Treatment of Pruritus Associated with Chronic Kidney Disease and Cholestasis.

Itching is an unpleasant sensation that provokes the desire to scratch. In general, itching is caused by dermatologic diseases, but it can also be caused by systemic diseases. Since itching hampers patients' quality of life, it is important to understand the appropriate treatment and pathophysiology of pruritus caused by systemic diseases to improve the quality of life. Mechanisms are being studied through animal or human studies, and various treatments are being tested through clinical trials. We report current trends of two major systemic diseases: chronic kidney disease and cholestatic liver disease. This review summarizes the causes and pathophysiology of systemic diseases with pruritus and appropriate treatments. This article will contribute to patients' quality of life. Further research will help understand the mechanisms and develop new strategies in the future.

Particulate matter 2.5 induces the skin barrier dysfunction and cutaneous inflammation via AhR- and T helper 17 cell-related genes in human skin tissue as identified via transcriptome analysis.

Particulate matter (PM2.5) is an environmental pollutant causing skin inflammatory diseases via epidermal barrier damage. However, the mechanism and related gene expression induced by PM2.5 remains unclear. Our aim was to determine the effect of PM2.5 on human skin tissue ex vivo, and elucidate the mechanism of T helper 17 cell-related inflammatory cytokine and skin barrier function. We verified the expression levels of gene in PM2.5-treated human skin tissue using Quantseq (3' mRNA-Seq), and Gene Ontology (GO) terms and protein-protein interaction (PPI) networks were performed. The PM2.5 treatment significantly enhanced the expression of Th 1, 2, 17 and 22 cell-related genes (cut-off value: │1.2 │ > fold change and p < 0.05). Most of all, Th17 cell-related genes are upregulated and those genes are associated with skin epidermal barrier function and Aryl hydrocarbon receptor (AhR), a xenobiotic receptor, pathway. In human keratinocyte cell lines, AhR-regulated genes (e.g. AhRR, CYP1A1, IL6 and IL36G), Th17 cell-related genes (e.g. IL17C) and epidermal barrier-related genes (e.g. SPRR2A and KRT71) are significantly increased after PM2.5. In the protein level, the secretion of IL-6 and IL-36G was increased in human skin tissue following PM2.5 treatment, and the expression of SPRR2A and KRT71 was significantly increased. PM2.5 exposure could ruin the skin epidermal barrier function via AhR- and Th17 cell-related inflammatory pathway.

Exosomes released by environmental pollutant-stimulated Keratinocytes/PBMCs can trigger psoriatic inflammation in recipient cells via the AhR signaling pathway.

Introduction: Exosomes, pivotal in intercellular communication during skin disease pathogenesis, have garnered substantial attention. However, the impact of environmental pollutants, such as benzo[a]pyrene (BaP) and 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD), on exosome release amid inflammatory skin diseases remains unexplored. This study addresses this gap by examining the influence of BaP and TCDD on exosome function, specifically focusing on immune-related pathway alterations in normal recipient keratinocytes and peripheral blood mononuclear cells (PBMCs). Methods: HaCaT cells were treated with exosomes from BaP- or TCDD-treated keratinocytes. Proinflammatory cytokines and chemokines, including TNF-α, IL-1ß, IL-6, IL-8, CXCL1, and CXCL5, were assessed. The involvement of the p65NF-κB/p38MAPK/ERK signaling pathway in recipient keratinocytes was investigated. Aryl hydrocarbon receptor (AhR) silencing was employed to elucidate its role in mediating the proinflammatory response induced by exosomes from BaP- or TCDD-treated keratinocytes. Results and discussion: Treatment with exosomes from BaP- or TCDD-treated keratinocytes induced a significant increase in proinflammatory cytokines and chemokines in HaCaT cells. The upregulation implicated the p65NF-κB/p38MAPK/ERK signaling pathway. AhR silencing attenuated this response, suggesting a role for AhR in mediating this response. In PBMCs from healthy controls, exosomes from BaP-stimulated PBMCs of psoriatic patients led to increased expression of proinflammatory cytokines and modulation of Th1/Th17 cell distribution via AhR activation. These findings unveil a novel dimension in the interplay between environmental xenobiotic agents (BaP and TCDD) and exosomal functions. The study establishes their influence on psoriatic inflammatory responses, shedding light on the underlying mechanisms mediated through the AhR signaling pathway in recipient keratinocytes and PBMCs.

TRPV3 and Itch: The Role of TRPV3 in Chronic Pruritus according to Clinical and Experimental Evidence.

Itching is a sensory phenomenon characterized by an unpleasant sensation that makes you want to scratch the skin, and chronic itching diminishes the quality of life. In recent studies, multiple transient receptor potential (TRP) channels present in keratinocytes or nerve endings have been shown to engage in the propagation of itch signals in chronic dermatological or pruritic conditions, such as atopic dermatitis (AD) and psoriasis (PS). TRPV3, a member of the TRP family, is highly expressed in the epidermal keratinocytes. Normal TRPV3 signaling is essential for maintaining epidermal barrier homeostasis. In recent decades, many studies have suggested that TRPV3 contributes to detecting pruritus signals. Gain-of-function mutations in TRPV3 in mice and humans are characterized by severe itching, hyperkeratosis, and elevated total IgE levels. These studies suggest that TRPV3 is an important channel for skin itching. Preclinical studies have provided evidence to support the development of TRPV3 antagonists for treating inflammatory skin conditions, itchiness, and pain. This review explores the role of TRPV3 in chronic pruritus, collating clinical and experimental evidence. We also discuss underlying cellular and molecular mechanisms and explore the potential of TRPV3 antagonists as therapeutic agents.

Relationships of Serum Homocysteine, Vitamin B12, and Folic Acid Levels with Papulopustular Rosacea Severity: A Case-Control Study.

Background: Rosacea is a chronic inflammatory skin disease with a multifactorial etiology. Recently, associations between serum homocysteine (Hcy) levels and inflammatory skin diseases, such as psoriasis and hidradenitis suppurativa, have been reported. However, no study has explored the levels of serum Hcy, folic acid, and vitamin B12 in patients with rosacea. Objective: To investigate serum Hcy, vitamin B12, and folic acid levels in patients with papulopustular rosacea (PPR), we characterized the association of these levels with PPR severity. Methods: This case-control study included 138 PPR patients and 58 healthy controls. The serum levels of Hcy, vitamin B12, and folic acid were measured. A correlation was assessed between disease severity and serum levels of Hcy, vitamin B12, and folic acid. Results: Serum vitamin B12 and folic acid levels were significantly lower in PPR patients than in the healthy controls (p = 0.011 and p = 0.0173, respectively). Although serum Hcy levels did not significantly differ between PPR patients and healthy controls, PPR severity was positively correlated with serum Hcy levels (p < 0.001). Conclusions: Our results suggest a possible association between hyperhomocysteinemia and vitamin B12 deficiency in patients with PPR.

Moisturizer in Patients with Inflammatory Skin Diseases.

As interest in skin increases, the cosmetic market is also growing. It is difficult to choose between the numerous types of basic cosmetics on the market. This article aims to provide advice and guidance on which products to recommend according to a patient's skin condition. Appropriate application of a moisturizer attempts not only to improve the dryness, but also improve the skin's natural barrier function to protect the skin from internal and external irritants to keep the skin healthy. Moisturizers consist of various ingredients, including occlusive agents, emollients, humectants, lipid mixture, emulsifiers, and preservatives. Pathophysiology of dry skin is also discussed to provide readers with the background they need to choose the right moisturizer for themselves. As moisturizers play an important role as adjuvant in the treatment of common skin diseases, such as atopic dermatitis, contact dermatitis, psoriasis, acne and rosacea, which type of moisturizer is appropriate for each disease was also dealt with. Basic cosmetics, especially moisturizers, should be recommended in consideration of the ingredients, effectiveness and safety of each product, and the skin condition of each patient.

Darier Disease with Psoriasis.

Darier disease is an autosomal dominant disorder with dark crusty patches and is classified as hereditary acantholytic dermatosis. Keratotic papules and crust are often present on the scalp, forehead, chest, back, upper arms, elbows, groin, and behind the ears, predominantly in seborrheic areas. A 48-year-old male patient presented skin lesions with pruritus on the trunk and both upper and lower extremities. He first noticed the lesion 15 years before. On physical examination, there were multiple erythematous papules with crust on the trunk and red-brown colored keratotic plaque on both extremities. The suspected histopathological diagnosis was psoriasis vulgaris. The patient's skin lesions and pruritus were significantly improved after the psoriasis treatment. While continuing psoriasis treatment, the patient showed sudden worsening of the skin lesions on the scalp, abdomen, and fingernails (V-shaped nicks) with pruritus. Punch biopsy was performed on the abdominal lesion again and the final diagnosis was Darier disease. The patient was then treated using alitretinoin while maintaining the use of guselkumab for psoriasis. There are only a few cases that we found in which patients with Darier disease also had psoriasis. We report this rare case of Darier disease with psoriasis and propose that an additional biopsy might be necessary for accurate diagnosis and proper treatment.

Effects of Autophagy Modulators and Dioxin on the Expression of Epidermal Differentiation Proteins on Psoriasis-Like Keratinocytes in vitro and ex vivo.

Objective: Psoriasis is a chronic inflammatory skin disorder associated with impairment of epidermal differentiation. Many signaling pathways, including those involved in aryl hydrocarbon receptor (AHR) and autophagy dysfunction, are reportedly associated with the pathogenesis of psoriasis. However, the discrete effects of dioxin via AHR activation or autophagy on the epidermal barrier remain unclear. In the current study, we evaluated the effects of autophagy modulators (chloroquine [CQ] and rapamycin) and the AHR agonist TCDD on the expression of epidermal barrier proteins in psoriasis-like keratinocytes and psoriasis lesional skin tissue culture. Methods: Polycytokine-stimulated human keratinocytes and psoriasis skin biopsies were treated with TCDD, CQ, or rapamycin, and the expression of keratinocyte differentiation-related factors, such as S100A7, S100A8, HRNR, IVL, FLG, and KRT10, was examined by Western blotting or quantitative-polymerase chain reaction. Results: TCDD upregulated S100A7 and S100A8 expression in polycytokine-stimulated HaCaT cells compared to that in unstimulated cells. CQ decreased HRNR, IVL, and KRT10 mRNA levels, while rapamycin increased HRNR, IVL, and KRT10 mRNA levels in HaCaT cells relative to that in unstimulated cells. Co-treatment with CQ reversed TCDD-induced elevation in FLG, HRNR, and IVL mRNA expression. In psoriasis skin tissue, TCDD induced the upregulation of HRNR, IVL, S100A7, and S100A8 compared with that in normal skin. In ex vivo cultures treated with CQ, IVL expression in psoriasis skin tissue was repressed compared to that in normal skin tissue. Conclusion: Our data suggest that autophagy modulation or AHR activation affects processes involved in epidermal differentiation and relates to the pathogenesis of chronic inflammatory skin diseases with skin barrier abnormalities such as psoriasis.

Aryl Hydrocarbon Receptors: Evidence of Therapeutic Targets in Chronic Inflammatory Skin Diseases.

The aryl hydrocarbon receptor (AhR), a ligand-dependent transcription factor, is important for xenobiotic metabolism and binds to various endogenous and exogenous ligands present in the skin. AhR is known to be associated with diseases in various organs; however, its functions in chronic inflammatory skin diseases, such as atopic dermatitis (AD) and psoriasis (PS), have recently been elucidated. Here, we discuss the molecular mechanisms of AhR related to chronic inflammatory skin diseases, such as AD and PS, and the mechanisms of action of AhR on the skin immune system. The importance of AhR molecular biological pathways, clinical features in animal models, and AhR ligands in skin diseases need to be investigated. In conclusion, the therapeutic effects of AhR ligands are demonstrated based on the relationship between AhR and skin diseases. Nevertheless, further studies are required to elucidate the detailed roles of AhR in chronic inflammatory skin diseases.