Inflammatory features of melasma lesions in Asian skin

Different therapeutic approaches in melasma: advances and limitations

Melasma is a chronic hyperpigmentation skin disorder that is more common in the female gender. Although melasma is a multifactorial skin disorder, however, sun-exposure and genetic predisposition are considered as the main etiologic factors in melasma occurrence. Although numerous topical and systemic therapeutic agents and also non-pharmacologic procedural treatments have been considered in melasma management, however, the commonly available therapeutic options have several limitations including the lack of sufficient clinical effectiveness, risk of relapse, and high rate of unwanted adverse drug reactions. Recruitment of nanotechnology for topical drug delivery in melasma management can lead to enhanced skin penetration, targeted drug delivery to the site of action, longer deposition at the targeted area, and limit systemic absorption and therefore systemic availability and adverse drug reactions. In the current review, first of all, the etiology, pathophysiology, and severity classification of melasma have been considered. Then, various pharmacologic and procedural therapeutic options in melasma treatment have been discussed. Afterward, the usage of various types of nanoparticles for the purpose of topical drug delivery for melasma management was considered. In the end, numerous clinical studies and controlled clinical trials on the assessment of the effectiveness of these novel topical formulations in melasma management are summarized.

Characteristics of dermal vascularity in melasma and solar lentigo

BACKGROUND /PURPOSE

Melasma and solar lentigo (SL) are major benign hyperpigmented lesions, and both have been shown to involve the dermal vasculature. This review discusses current knowledge regarding the clinical characteristics of dermal vascularity in melasma and SL, as well as the results of relevant molecular biological investigations.

METHODS

PubMed and Google Scholar were searched in December 2023 to identify articles related to melasma, SL, and the dermal vasculature in these lesions.

RESULTS

Vascular morphologies in melasma and SL have been detected by histological and non-invasive methods, including modalities such as optical coherence tomography. Biological studies have indicated that factors secreted from vascular endothelial cells, such as stem cell factor and endothelin-1, can promote melanogenesis. With respect to phototherapy, blood vessel-targeting laser treatments are expected to provide long-term suppression of pigmentation, but this regimen is only effective when dilated capillaries are visible.

CONCLUSION

In both melasma and SL, clinical and experimental investigations are revealing the contributions of dermal vascularity to hyperpigmentation. More effective treatment may require identification of hyperpigmentation subtypes. In the future, knowledge of treatment (including phototherapy) is expected to accumulate through reliable and validated non-invasive measurements.

The efficacy and safety of microneedling with topical tranexamic acid for melasma treatment: A systematic review and meta-analysis

OBJECTIVE

Microneedling with topical tranexamic acid (TXA) is a novel treatment option for melasma; however, the efficacy and safety of this combined administration therapy is in controversial. This study is conducted to address this issue of this technique in melasma.

METHODS

An extensive literature review was performed to identify relevant trials, including randomized split-face studies, randomized controlled trials and prospective non-randomized split-face studies, comparing microneedling plus topical TXA to routine treatments or placebo. The primary outcomes were changes of the Melasma Area Severity Index (MASI)/modified MASI (mMASI)/hemi MASI between before and after treatment, as well as the changes between a particular treatment and microneedling plus TXA. The mean differences (MDs) and 95% confidence intervals (CIs) were calculated for the reduction of melasma severity scores from baseline to each time point. In contrast, the standard mean differences (SMDs) and 95% CIs were calculated for the differences in reduction in melasma severity scores between the experimental and control groups at each time point.

RESULTS

A total of 16 trials were included in the systematic review and data synthesis. The pooled analysis demonstrated that MASI, mMASI, and hemiMASI scores decreased significantly at 4 weeks (MD = 1.85; 95% CI = 1.15-2.54), 8 weeks (MD = 3.28; 95% CI = 2.31-4.24), 12 weeks (MD = 4.73; 95% CI = 2.79-6.50), 16 weeks (MD = 3.18; 95% CI = 1.50-4.85), and 20 weeks (MD = 3.20; 95% CI = 1.95-4.46) after treatment when compared with baseline. The reduction in melasma severity scores of microneedling with TXA group at 4 weeks was more significant than the routine treatment group (SMD = 0.97; 95% CI = 0.09-1.86), while insignificant at 8 weeks (SMD = 1.21; 95% CI = -0.17 to 2.59), 12 weeks (SMD = 0.63; 95% CI = -0.03 to 1.29), 16 weeks (SMD = 0.61; 95% CI = -2.85 to 4.07), or 20 weeks (SMD = 1.04; 95% CI = -1.28 to 3.36).

CONCLUSION

Despite the high heterogeneity across these studies, the current findings indicated that microneedling with topical TXA is an alternative treatment option for melasma treatment; and more well-designed studies are needed to confirm it.

Safety and efficacy of superficial micro-focused ultrasound with visualization for melasma in Asians: An uncontrolled pilot study

BACKGROUND

The pathophysiology of melasma is multifactorial, resulting in treatment resistance and a high recurrence rate. Recent research suggests that focused ultrasound might treat melasma effectively.

OBJECTIVES

To investigate the efficacy and safety of superficial micro-focused ultrasound with visualization (MFU-V) for melasma in Asians.

METHODS

Patients (n = 20) with mixed melasma on both cheeks received 2 MFU-V treatments spaced 1 month apart. At monthly visits over 5 months, treatment efficacy and safety were evaluated. Standardized photographs were clinically assessed using the modified Melasma Area and Severity Index (mMASI), and 6-point grading scales for melasma lightening and area of involvement. Patients provided pain, global aesthetic improvement scale (GAIS), and satisfaction assessments.

RESULTS

In 40 cheeks, the mean mMASI score was significantly reduced from 13.2 at baseline to 2.4 at month 4, and 2.8 at month 5. Twenty-nine cheeks (72.5%) showed lightening of melasma at month 4 that persisted until month 5, with improvements up to 75% compared to baseline. Melasma area decreased overall, with sites containing >30% melasma involvement decreasing from 55% to 20% by month 5, and none with 70%-89% involvement. Melasma lightening and area improved visibly in 40% and 20% of cheeks, respectively, as early as 1 month after index MFU-V treatment. Improvements continued after the second treatment and persisted until study closure, correlating with patient GAIS and satisfaction scores. Procedure was well tolerated with only mild-to-moderate pain reported in 92.5% of treatments.

CONCLUSION

Superficial MFU-V is a safe and effective treatment for melasma.

Post-Inflammatory Hyperpigmentation in Dark Skin: Molecular Mechanism and Skincare Implications

Human skin is characterized by significant diversity in color and tone, which are determined by the quantity and distribution of melanin pigment in the epidermis. Melanin absorbs and reflects ultraviolet radiation (UVR), preventing the damage to genomic DNA in the epidermis and degradation of collagen in the dermis; therefore, darker skin types are thought to be well protected from the photodamage because of the high melanin content. However, increased content of melanin in combination with the extrinsic stress factors causing inflammation such as excess UVR, allergic reactions, or injury can also frequently lead to cosmetic problems resulting in discoloration and scarring. This review summarizes current knowledge on histopathology and likely molecular signatures of one of the most common problems, post-inflammatory hyperpigmentation (PIH). The mechanisms proposed so far are subsequently discussed in the context of other factors characterizing darker skin types. This includes the common cellular features, organization of upper skin layers, and major biomarkers, with particular emphasis on increased propensities to systemic and localized inflammation. Enhanced or prolonged inflammatory responses can not only affect the process of melanogenesis but also have been implicated in injury-related skin pathologies and aging. Finally, we summarize the major cosmetic treatments for PIH and their known anti-inflammatory targets, which can be beneficial for darker skin tones and combined with broad-spectrum filters against UVR.

Medical therapies for Melasma

Melasma is a common malady affecting all races with a higher incidence in Hispanics, Middle Eastern, Asians and African origin females (Fitzpatrick skin phototypes III-V). Women are affected much more often than men. Melasma remains a significant cause of cosmetic morbidity and psychosocial embarrassment affecting quality of life necessitating effective and reliable treatment. Unfortunately, treatment remains unsatisfactory due to limited efficacy, adverse effects and relapses after stopping treatment. Although chemical peels, laser and light therapies and dermabrasion may have utility, the evidence available for their efficacy is limited and they often cause post inflammatory hyperpigmentation particularly in individuals with darker skin types. Medical therapies remain mainstay in the management of melasma. The triple combination, hydroquinone 4%, tretinoin 0.05% and fluocinolone acetonide 0.01% (Triluma, Galderma, Ft. Worth Texas, often modified incorporating different corticosteroids) remains the only US FDA approved treatment for melasma and is the gold standard due its demonstrated efficacy across ethnicities. Oral tranexamic acid alone or in combination with other modalities has also shown significant efficacy. Several cosmeceuticals and botanical extracts used as skin lightening agents have been demonstrated to be useful. Physical sunscreens containing zinc oxide, iron oxide, titanium dioxide, and silicones provide photoprotective and camouflage effect. We propose that a multimodality approach to the treatment of melasma is the most effective treatment approach. This review is focused on the medical therapies for melasma.

Efficacy and Safety of Topical Therapy With Botanical Products for Melasma: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Botanical products have been increasingly popular in topical therapies for melasma, as presumed safer and milder than fully synthetic products. Although the efficacy of different topical botanicals has recently been substantiated through randomized controlled trials (RCTs), there is a lack of sufficiently pooled evidence on their efficacy and safety for the treatment of melasma. Herein, a systematic review and meta-analysis was conducted on the efficacy and safety of topical botanical products for the treatment of melasma, following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). All RCTs on the use of topical botanical products for the treatment of melasma in humans were included, except for trials enrolling pregnant patients. The primary outcome was Melasma Area and Severity Index (MASI) or its variation. The secondary outcomes included Mexameter^® reading, melasma improvement evaluated by participants, and any reported adverse events (AEs). As a result, twelve eligible trials comprising 695 patients with melasma from 6 different countries were included. The topical botanical products contained active ingredients which varied among trials as follows: herb-derived molecule, extracts of a single herb, and extracts of compound herbs. Topical therapy with botanical products significantly improved melasma with a large effect on MASI reduction (SMD −0.79, 95% CI −1.14 to −0.44, p < 0.00001), and a moderate effect on Mexameter^® reading reduction (SMD −0.52, 95% CI −0.81 to 0.23, p = 0.0005), when compared with placebo. It also showed a similar improvement of melasma with a better safety profile (RR 0.37, 95% CI 0.15–0.88, p = 0.02), when compared with active-comparators. Botanical products were well-tolerated across studies, with no serious AEs reported. Despite the limitations such as small sample size, short duration of follow up and varied botanical products, this work still represents the best level of evidence currently available on topical use of botanical products on melasma. Moreover, it should be noted that more well-designed studies are needed before recommending topical botanical products as a viable treatment option for melasma.

Dermal Pathology in Melasma: An Update Review

BACKGROUND

Melasma is a complex and multipathophysiological condition that is challenging to treat. The roles of each element in the dermis were highlighted in this recent year due to targeting it with emerging therapies. Although some studies have demonstrated abnormal findings in the dermis of melasma lesions, there are no integrated data regarding these findings.

PURPOSE

This article aims to discuss each finding in the dermis of melasma lesions and to provide some ideas about treatment options.

METHODS

An Internet search was completed using the MEDLINE, Embase, Scopus, and Google Scholar databases for relevant literature through June 2021 and reference lists of respective articles. Only the articles published in English language were included.

RESULTS

Several studies have focused on the dermal changes in melasma. Common findings included basement membrane disruption, pendulous melanocytes, marked solar elastosis, increased melanophages, increased mast cells, and neovascularization. In addition, each of them had the specified mechanism that may relate with the others.

CONCLUSION

Several changes in the dermis of melasma lesion may be connected with pathological changes in the epidermis. This may serve as a potential target treatment for melasma, which requires a multimodal approach.

Efficacy and Safety of Oral Herbal Drugs Used as Adjunctive Therapy for Melasma: A Systematic Review and Meta-Analysis of Randomised Controlled Trials

Background

Melasma is an acquired disorder of facial pigmentation. Its etiology is multifactorial; thus, the management is usually challenging. As a complementary therapy, herbal drugs are often used in the management of melasma. This work was aimed to investigate the efficacy and safety of herbal drugs on melasma in female patients.

Methods

This study followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A comprehensive search was conducted, and all randomised controlled trials (RCTs) on the use of oral herbal drugs as complementary therapy for melasma in female patients were included. A meta-analysis was conducted according to the guidelines of the Cochrane Collaboration using Review Manager 5.4.

Results

Ten eligible trials, with 1015 female melasma patients, were included. All of the included RCTs had some concerns for risk of bias for different reasons, especially for that most of included trials were unblinded. Pooled data suggested phytotherapy plus routine therapy had significantly better efficacy on melasma than routine therapy, in terms of response rate (OR: 4.49, 95% CI: 3.25 to 6.20, p < 0.00001), reduction of skin lesion score (SMD: −0.56, 95% CI: −0.79 to −0.33, p < 0.00001), and improvement of serum E2 levels (SMD: −1.58, 95% CI: −2.62 to −0.55, p 0.003). In addition, there was no significant difference in the incidence of AEs between phytotherapy plus routine therapy and routine therapy (OR: 0.92, 95% CI: 0.53 to 1.58; p 0.76). Overall, herbal drugs used as an adjunct to routine therapy significantly enhanced the efficacy for the treatment of melasma but with a comparable safety profile.

Conclusion

These findings have implications for recommending herbal drugs as a viable complementary treatment option for melasma.

Lasers, lights, and compounds for melasma in aesthetics

Melasma is a chronic and relapsing skin condition. Although melasma is usually asymptomatic, it can be associated with immense psychosocial stress and greatly impact a patient's quality of life. Over the years, many different treatments have been used, ranging from daily photoprotection, topical lightening creams, and oral agents to laser and light-based therapies; however, efficacy is often limited with such treatments, and there is currently no effective modality to prevent recurrence. Although treatment strategies had originally centered on the use of hydroquinone, newer modalities now include oral tranexamic acid and lasers. We examined previous and ongoing debates related to melasma treatments and have reviewed the current efficacy and safety of available treatments. Critical components essential to the successful management of melasma are the setting of patient expectations and assurance of treatment compliance.

Guanine Deaminase in Human Epidermal Keratinocytes Contributes to Skin Pigmentation

Epidermal keratinocytes are considered as the most important neighboring cells that modify melanogenesis. Our previous study used microarray to show that guanine deaminase (GDA) gene expression is highly increased in melasma lesions. Hence, we investigated the role of GDA in skin pigmentation. We examined GDA expression in post-inflammatory hyperpigmentation (PIH) lesions, diagnosed as Riehl’s melanosis. We further investigated the possible role of keratinocyte-derived GDA in melanogenesis by quantitative PCR, immunofluorescence staining, small interfering RNA-based GDA knockdown, and adenovirus-mediated GDA overexpression. We found higher GDA positivity in the hyperpigmentary lesional epidermis than in the perilesional epidermis. Both UVB irradiation and stem cell factor (SCF) plus endothelin-1 (ET-1) were used, which are well-known melanogenic stimuli upregulating GDA expression in both keratinocyte culture alone and keratinocyte and melanocyte coculture. GDA knockdown downregulated melanin content, while GDA overexpression promoted melanogenesis in the coculture. When melanocytes were treated with UVB-exposed keratinocyte-conditioned media, the melanin content was increased. Also, GDA knockdown lowered SCF and ET-1 expression levels in keratinocytes. GDA in epidermal keratinocytes may promote melanogenesis by upregulating SCF and ET-1, suggesting its role in skin hyperpigmentary disorders.

Therapeutic efficacy and safety of oral tranexamic acid 250 mg once a day versus 500 mg twice a day: a comparative study

Oral tranexamic acid (TXA) 250 mg twice daily has been used effectively for 4 weeks to 6 months to treat melasma. As relapses are frequent on discontinuation, a minimum effective dose of TXA that can be used safely for long time remains unknown. We compared the efficacy of oral TXA 250 mg once daily and 500 mg twice daily given for 16 weeks in 132 (m:f 23:109) adults with melasma. 42 patients in Group-A (TXA 250 mg/d) and 46 patients in Group-B (TXA 500 mg twice/d) completed the study. They were followed up at 4-week interval for percentage reduction in baseline Melasma Area Severity Index (MASI) and at 24 and 28 weeks for relapse. Therapeutic response, for both as per-protocol and intention-to-treat analysis, was scored as very good (> 75% reduction), good (51-75% reduction), moderate (25-50% reduction), mild (< 25% reduction) or no improvement. Reduction in mean MASI score at 4 weeks was not statistically significant in Group-A but it decreased significantly 8 weeks onwards and was comparable with that in Group-B. The relapse rate was higher in Group-B (10.8%) than Group-A (4.7%) at the end of 28 weeks. Oligomenorrhoea and abdominal discomfort in few patients did not necessitate treatment discontinuation. TXA 500 mg twice daily showed early reduction in mean MASI score compared to 250 mg given once daily with comparable safety and therapeutic efficacy at 16 weeks. Open-label cross-sectional design, no control arm, small number of patients in each group, MASI score being subjective assessment tool, short duration of treatment and follow-up are study limitations.

Clinical improvement of photoaging-associated facial hyperpigmentation in Korean skin with a picosecond 1064-nm neodymium-doped yttrium aluminum garnet laser

Traditional attempts at alleviating photoaging-associated facial pigmentation conditions such as melasma, mottled hyperpigmentation, and post-inflammatory hyperpigmentation have yielded disfiguring cosmetic results. Laser toning using a low-fluence Q-switched 1064-nm neodymium-doped yttrium aluminum garnet (Nd:YAG) laser has been more commonly applied to date. However, the treatment efficacy and safety of this approach have not been widely reported. This study therefore evaluated the efficacy and safety of picosecond 1064-nm Nd:YAG laser application for photoaging-associated facial pigmentation treatment in Korean subjects. Forty-seven Korean subjects with photoaging-associated facial pigmentation underwent picosecond 1064-nm laser application. The clinical improvement of 17 patients was assessed by objective measurements such as melanin and erythema indices. All subjects received six biweekly treatments with the laser in a three-pass fashion delivering approximately 2000 to 2500 shots using a zoom handpiece with a spot size of 7 mm, fluence ranging from 0.4 to 0.7 J/cm², and a repetition rate of 10 Hz. Clinicians evaluated the improvement of pigmentation using the pigmentation area and severity index (PSI), and subjects reported their satisfaction level on a four-point scale. Statistical analyses were performed using the SPSS version 19.0 for Windows software program (IBM Corp., Armonk, NY, USA). Forty-seven subjects (45 females and two males) completed this study with a 12-week follow-up period. The average decrease in PSI value at 12 weeks after treatment was 6.85 ± 6.35 points (p < 0.001). The average decreases in the values of the erythema and melanin indices were 19.41 ± 64.64 points (p = 0.234) and 28.88 ± 32.89 points (p = 0.002). An analysis of 32 subjects' reports (68.1%) suggested good or excellent improvement. No serious adverse effects were observed during treatment or the follow-up period. Picosecond 1064-nm Nd:YAG laser application appears to be safe and effective in improving various photoaging-associated facial pigmentation conditions in Korean skin.

A cream of herbal mixture to improve melasma

Background

Melasma is an acquired, common hyperpigmented disorder on the face. While many therapeutic approaches are available, their efficacy is moderate.

Objective

To investigate the safety and efficacy of a cream containing herbal mixture for melasma.

Methods

A total of 90 volunteers with melasma were enrolled in this randomized, double‐blind, controlled clinical study, and they were randomly divided into three groups (A, B, and C). Patients in group A were treated with a cream containing herbal mixture, while groups B and C were treated with arbutin cream and placebo, respectively, twice daily for 12 weeks. Melasma area and severity index (MASI) score, melanin index (MI), erythema index (EI), changes in density of inflammatory cells, and adverse events were evaluated every 4 weeks.

Results

Although MASI scores declined significantly in both groups A and B (P < 0.05), a greater reduction was seen in group A (13.00−9.82 = 3.18 for group A; 12.65−10.84 = 1.81 for group B). Moreover, the cream containing herbal mixture, but not arbutin cream and placebo, significantly reduced EI and density of inflammatory cells after 12‐week treatment (P < 0.05). No adverse reactions were observed in either group A or group C. In group B, two subjects experienced mild erythema and itching, which disappeared after stop using the arbutin cream.

Conclusion

The cream containing herbal mixture is safe and effective for melasma.

Loratadine, an H1 Antihistamine, Inhibits Melanogenesis in Human Melanocytes

It has long been believed that histamine is associated with cutaneous melanogenesis. Specifically, H2-receptor antagonists reportedly inhibit melanogenesis, but H1-receptor antagonists, which are some of the most commonly prescribed medicines in dermatology, have not been studied to determine whether and how they regulate melanogenesis. Therefore, we screened H1-receptor antagonists to determine whether they inhibit melanogenesis and found that loratadine was particularly effective, in this regard without compromising cellular viability. Loratadine downregulated microphthalmia-associated transcription factor (MITF) and tyrosinase in melanocytes. To determine the intracellular signaling pathways, Akt was consistently activated by loratadine. PI3K/Akt pathway inhibitor, LY294002, restored the reduced melanin content that was induced by loratadine. In addition, phospho-GSK-3β also was found to be increased following loratadine treatment. Loratadine reduced the amount of PKC-βII in the membrane fraction, thereby decreasing its activity. Taken together, our data indicate that loratadine regulates melanogenesis via Akt/MITF and PKC-βII signaling, thereby leading to the inhibition of melanogenic proteins. The antimelanogenic effects of loratadine have potentially significant and useful roles in dermatologic practice, although further clinical studies will be required to test this.

Novel regulation of melanogenesis by adiponectin via the AMPK/CRTC pathway

Several studies observed that adiponectin, an important adipokine that improves glucose metabolism by regulating AMP-activated protein kinase (AMPK) signaling, is dermatologically beneficial. In our recent microarray data, we found that adiponectin expression was lower in lesional skin than in non-lesional skin of melasma patients. Given that AMPK is a key adiponectin signaling mediator, we investigated the role of adiponectin and AICAR, a cell-permeable AMPK activator, in melanogenesis. We herein showed that adiponectin and AICAR downregulated MITF, tyrosinase, TRP-1, and DCT expression and reduced melanin content in normal human and mouse melanocytes. The depigmenting effect of adiponectin was mediated via AMPK activation, which induced the inhibitory phosphorylation of CREB-regulated transcription co-activators (CRTCs) and subsequent suppression of the novel CRTC/CREB pathway in melanocytes. These findings suggest that adiponectin and its analogs are useful as a clinical strategy for treating hyperpigmentation disorders.

A prospective, split-face, double-blinded, randomized study of the efficacy and safety of a fractional 1064-nm Q-switched Nd:YAG laser for photoaging-associated mottled pigmentation in Asian skin

BACKGROUND

Laser toning using low-fluence 1064-nm Q-switched neodymium-doped yttrium aluminum laser (QSNY) has gained popularity in the treatment of photoaging-associated mottled pigmentation (PMP). However, hypopigmentation or lack of efficacy has been reported depending on the fluences used.

OBJECTIVE

To compare a novel fractional 1064-nm QSNY with conventional 1064-nm QSNY for the treatment of photoaging-associated mottled pigmentary lesions except epidermal lesions of lentigines and freckles through a randomized, split-face, double-blind study.

MATERIALS AND METHODS

Thirteen Asian women were treated every week for 6 weeks with fractional 1064-nm QSNY on one side of the face and conventional 1064-nm QSNY on the other side. We evaluated the pigmentation area and severity index (PSI), melanin index, erythema index, and the patient's global assessment of improvement.

RESULTS

At three months post-treatment, the PSI score improved compared with baseline, by 14.48% on the conventional 1064-nm QSNY side and 21.81% on the fractional 1064-nm QSNY side. Both groups showed improvements in the melanin index.

CONCLUSION

Both fractional 1064-nm QSNY and strictly low-fluence conventional 1064-nm QSNY are moderately effective against PMP and other photoaging signs. Fractional laser toning shows better subjective outcomes than conventional toning.

The Effect of MCP-1/CCR2 on the Proliferation and Senescence of Epidermal Constituent Cells in Solar Lentigo

Solar lentigo (SL) is a representative photoaging skin disorder. Alteration of the main epidermal constituent cells-keratinocytes and melanocytes-in relation to the photoaged dermal environment or chemokine/cytokine network is suggested as its pathogenesis. Among these, we focused on monocyte chemoattractant protein-1 (MCP-1), as it is known to be associated with tissue aging. For the first time, we report that the MCP-1 receptor, CCR2, is expressed in normal human melanocytes. In SL tissue, there was an increase of CCR2+Melan A+ melanocytes with positivity to Rb protein compared to peri-lesional normal skin. MCP-1 induced the proliferation of normal human melanocytes without a significant change in the melanin content. MCP-1 treatment in normal human keratinocytes showed an increase in senescence-associated β-galactosidase staining and p53 and p21 protein expressions. In summary, MCP-1 may participate in the development of SL by affecting epidermal constituent cells, for example, by inducing melanocyte proliferation and keratinocyte senescence.

Recent progress in melasma pathogenesis

Melasma is a common skin pigmentation condition. Given therapeutic difficulty as one of the biggest concerns, understanding of the etiology and pathogenesis of melasma becomes essential. UV irradiation, female sex hormones, and inflammatory processes are addressed as triggering factors with genetic predisposition. The mechanism of UV-induced melanogenesis has been extensively investigated as a model system to study melasma pathogenesis. Hitherto, treatment modalities for melasma are similar to other hyperpigmentation disorders. However, individual triggering factors induce a separate pigmentation disease, whose pathogenic mechanisms and clinical phenotypes are different from the ones encountered in melasma. Fortunately, there have been ongoing updates on melasma pathogenesis with regard to major triggering factors. Presence of certain factors working independently of UV exposure and role of dermal factors and microRNAs are being identified as novel discoveries about melasma pathogenesis. In this review, the melasma pathogenesis is reviewed in association with updated and new findings.