Photodynamic therapy with intralesional methylene blue and a 635 nm light-emitting diode lamp in hidradenitis suppurativa: a retrospective follow-up study in 7 patients and a review of the literature

Topical and Intralesional Therapies for Hidradenitis Suppurativa: A Systematic Literature Review

BACKGROUND AND OBJECTIVE

Topical and intralesional (IL) treatments may be considered the first-line therapy in patients with hidradenitis suppurativa (HS); however, the evidence supporting their use is limited. The aim of our review is to evaluate the efficacy and safety profile of topical and IL treatments in patients with HS.

MATERIALS AND METHODS

We designed a systematic review of the current medical literature available following the PICO(T) method. And including all types of studies (Study type [T]) of individuals with HS of any sex, age, and ethnicity (Population [P]) who received any topical or IL treatment for HS (Intervention [I]) compared to placebo, other treatments, or no treatment at all (Comparator [C]), and reported efficacy and/or safety outcomes (Outcomes [O]). Two outcomes were defined: quality of life and the no. of patients with, at least, one adverse event. The search was conducted in the Cochrane Library, MEDLINE, and Embase databases; study selection was performed based on pre-defined criteria. The risk of bias was determined in each study.

RESULTS

We obtained a total of 11,363 references, 31 of which met the inclusion criteria. These studies included 1143 patients with HS, 62% of whom were women. A total of 10, 8, 6, 2, and 5 studies, respectively, evaluated the use of photodynamic therapy (PDT), glucocorticoids, resorcinol, topical antibiotics, and other interventions. Most articles were case series (n=25), with only five randomized clinical trials (RCTs) and one cohort study. RCTs showed improvement in disease activity with topical clindamycin and botulinum toxin (BTX) vs placebo, and PDT with methylene blue (MB) niosomal vs free MB; however, intralesional triamcinolone acetonide was not superior to placebo. The risk of bias was low in three RCTs and high in two RCTs.

CONCLUSION

The quality of evidence supporting the use of topical, or IL treatments is low. However, it supports the use of topical clindamycin, PDT, and BTX. Well-designed RCTs with standardized outcomes and homogeneous populations of patients and lesions are needed to support decision-making in the routine clinical practice.

Topical and Intralesional Therapies for Hidradenitis Suppurativa: A Systematic Literature Review

BACKGROUND AND OBJECTIVE

Topical and intralesional (IL) treatments may be considered the first-line therapy in patients with hidradenitis suppurativa (HS); however, the evidence supporting their use is limited. The aim of our review is to evaluate the efficacy and safety profile of topical and IL treatments in patients with HS.

MATERIALS AND METHODS

We designed a systematic review of the current medical literature available following the PICO(T) method. And including all types of studies (Study type [T]) of individuals with HS of any sex, age, and ethnicity (Population [P]) who received any topical or IL treatment for HS (Intervention [I]) compared to placebo, other treatments, or no treatment at all (Comparator [C]), and reported efficacy and/or safety outcomes (Outcomes [O]). Two outcomes were defined: quality of life and the no. of patients with, at least, one adverse event. The search was conducted in the Cochrane Library, MEDLINE, and EMBASE databases; study selection was performed based on pre-defined criteria. The risk of bias was determined in each study.

RESULTS

We obtained a total of 11,363 references, 31 of which met the inclusion criteria. These studies included 1143 patients with HS, 62% of whom were women. A total of 10, 8, 6, 2, and 5 studies, respectively, evaluated the use of photodynamic therapy (PDT), glucocorticoids, resorcinol, topical antibiotics, and other interventions. Most articles were case series (n=25), with only five randomized clinical trials (RCTs) and one cohort study. RCTs showed improvement in disease activity with topical clindamycin and botulinum toxin (BTX) vs placebo, and PDT with methylene blue (MB) niosomal vs free MB; however, intralesional triamcinolone acetonide was not superior to placebo. The risk of bias was low in three RCTs and high in two RCTs.

CONCLUSION

The quality of evidence supporting the use of topical, or IL treatments is low. However, it supports the use of topical clindamycin, PDT, and BTX. Well-designed RCTs with standardized outcomes and homogeneous populations of patients and lesions are needed to support decision-making in the routine clinical practice.

aPDI meets PPE: photochemical decontamination in healthcare using methylene blue-where are we now, where will we go?

Personal protective equipment (PPE) reuse, first recommended in the context of the SARS-CoV-2 pandemic, can mitigate shortages in crisis situations and can greatly reduce the environmental impact of typically single-use PPE. Prior to safe reuse, PPE must be sanitized and contaminating pathogens-in current circumstances viruses in particular-must be inactivated. However, many established decontamination procedures are not equitable and remain unavailable in low-resource settings. In mid-2020, an interdisciplinary consortium of researchers first studied the potential of implementing cheap and easy-to-use antimicrobial photodynamic inactivation (aPDI) using methylene blue as photosensitizer to decontaminate face masks and filtering facepiece respirators. In this perspective piece, we describe the development of this novel method, discuss recent advances, and offer insights into how equitable PPE decontamination via methylene blue-based aPDI may be integrated into circular economy policies in the healthcare sector.

Laser and intense pulsed light in the treatment of hidradenitis suppurativa

Treatment of hidradenitis suppurativa (HS) requires a combination of medical, surgical, and lifestyle interventions. Intense pulsed light (IPL) and lasers have been reported to be useful. The aim of this review is to find the evidence supporting IPL and laser treatment of HS and to provide guidance for the management of specific HS lesions. We searched PubMed and Web of Science for "laser" and "hidradenitis suppurativa" on April 6, 2022. Inclusion criteria were >10 patients, reported follow-up, English language, and human subjects with a diagnosis of HS. A total of 724 articles were screened, but only 17 studies qualified for inclusion (IPL (n = 4), Nd:YAG (n = 6), CO2 laser (n = 6), and intralesional treatment (n = 2). The majority of the studies had a low (n = 10) or moderate (n = 7) evidence level. Treatment effect was noticed in studies using IPL and Nd:YAG (hair reduction). CO2 laser was used for surgery with a success rate ranging from 70.7% to 96.7%. CO2 laser is useful for surgery of stationary HS lesions, but it is difficult to draw a conclusion on the use of IPL and Nd:YAG (hair reduction) as the studies were too heterogeneous to perform a meta-analysis.

Gold-Polypyrrole-Loaded Eosin in Photo-Mediated Treatment of Hidradenitis Suppurativa: In Vivo Trans-Epidermal Permeation Study and Clinical Case Report

This study reports a new protocol for the management of Hidradenitis Suppurativa (HS), depending on the synergistic photodynamic and photothermal effect of eosin yellow-gold-polypyrrole hybrid nanoparticles (E-G-Ppy NPs). E-G-Ppy NPs and gold-polypyrrole NPs (G-Ppy NPs) were synthesized, characterized, and formulated in topical hydrogels. Then, in vivo trans-epidermal permeation study, under both dark and white light-irradiation conditions, was done on albino mice. The E-G-Ppy hydrogel was then applied on a twenty-four years old female with recurrent axillary HS lesions pretreated with fractional CO₂ laser. Thereafter, the treated lesions were irradiated sequentially, using an IPL system, in the visible (~550 nm) and NIR band (630-1100 nm) to activate the synthesized nanoparticles. Results showed that, upon application to mice skin, E-G-Ppy exhibited good tolerance and safety under dark conditions and induced degenerative changes into dermal layers after white-light activation, reflecting deep penetration. Photo-activation of E-G-Ppy hydrogel to a severe Hidradenitis Suppurativa case showed an improvement of 80% of the lesions according to average HS-LASI scores after 4 sessions with no recurrence during a follow-up period of six months. In summary, the dual photodynamic/photothermal activation of E-G-Ppy NPs can represent a promising modality for management of HS. Further expanded clinical studies may be needed.

Emerging Strategies in Enhancing Singlet Oxygen Generation of Nano-Photosensitizers Toward Advanced Phototherapy

The great promise of photodynamic therapy (PDT) has thrusted the rapid progress of developing highly effective photosensitizers (PS) in killing cancerous cells and bacteria. To mitigate the intrinsic limitations of the classical molecular photosensitizers, researchers have been looking into designing new generation of nanomaterial-based photosensitizers (nano-photosensitizers) with better photostability and higher singlet oxygen generation (SOG) efficiency, and ways of enhancing the performance of existing photosensitizers. In this paper, we review the recent development of nano-photosensitizers and nanoplasmonic strategies to enhance the SOG efficiency for better PDT performance. Firstly, we explain the mechanism of reactive oxygen species generation by classical photosensitizers, followed by a brief discussion on the commercially available photosensitizers and their limitations in PDT. We then introduce three types of new generation nano-photosensitizers that can effectively produce singlet oxygen molecules under visible light illumination, i.e., aggregation-induced emission nanodots, metal nanoclusters (< 2 nm), and carbon dots. Different design approaches to synthesize these nano-photosensitizers were also discussed. To further enhance the SOG rate of nano-photosensitizers, plasmonic strategies on using different types of metal nanoparticles in both colloidal and planar metal-PS systems are reviewed. The key parameters that determine the metal-enhanced SOG (ME-SOG) efficiency and their underlined enhancement mechanism are discussed. Lastly, we highlight the future prospects of these nanoengineering strategies, and discuss how the future development in nanobiotechnology and theoretical simulation could accelerate the design of new photosensitizers and ME-SOG systems for highly effective image-guided photodynamic therapy.

New perspectives on the treatment of hidradenitis suppurativa

Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease characterized by the presence of painful nodules, abscesses, chronically draining fistulas, and scarring in apocrine gland-bearing areas of the body. The exact pathogenesis of HS is not yet well understood, but there is a consensus in considering HS a multifactorial disease with a genetic predisposition, an inflammatory dysregulation, and an influence of environmental modifying factors. Therapeutic approach of HS is challenging due to the wide clinical manifestations of the disease and the complex pathogenesis. This review describes evidence for effectiveness of current and emerging HS therapies. Topical therapy, systemic treatments, biological agents, surgery, and light therapy have been used for HS with variable results. Adalimumab is the only US Food and Drug Administration (FDA) approved biologic agent for moderate-to-severe HS, but new therapeutic options are being studied, targeting different specific cytokines involved in HS pathogenesis. Comparing treatment outcomes between therapies is difficult due to the lack of randomized controlled trials. Treatment strategy should be selected in concordance to disease severity and requires combination of treatments in most cases.

Should We Scan Hidradenitis Suppurativa Patients? A Systematic Review of Radiologic Findings

OBJECTIVE

To bring awareness and close gaps between dermatologists and radiologists about the contribution of imaging techniques for diagnosis, treatment, and follow-up of hidradenitis suppurativa (HS).

DATA SOURCES

Investigators searched the PubMed database for articles on HS and radiology techniques.

STUDY SELECTION

Databases were searched up to December 2018. The query retrieved 257 publications, of which 103 were unique; of these, 7 were inaccessible. From the remaining 96, 33 were irrelevant (did not discuss HS lesion features). After applying the inclusion criteria, 63 studies were relevant to this study.

DATA EXTRACTION

A standardized form was constructed to extract data from eligible studies by two independent authors.

DATA SYNTHESIS

Imaging techniques are significant and useful tools in HS management. Imaging should be carried out to evaluate disease severity, subclinical features, treatment success, and intraoperative patient assessment. Providers should consider nonconventional radiology techniques, which are underused in clinical management of HS. Further, dermatology and radiology require a shared terminology of disease features to better understand patient status.

CONCLUSIONS

Publications on HS lesion imaging have increased over the years. Imaging techniques have proven useful for determining HS severity and treatment effectiveness, as well as intraoperative patient assessment. These authors strongly recommend the use of these techniques in routine clinical practice for patients with HS.

Ultrasound-guided photodynamic therapy with intralesional methylene blue and a 635 nm light-emitting diode lamp in hidradenitis suppurativa: A retrospective study of 41 patients

BACKGROUND

Photodynamic therapy for hidradenitis suppurativa (HS) is a therapeutic alternative with a good safety profile, but its effectiveness has yet to be demonstrated.

OBJECTIVES

To demonstrate the effectiveness of PDT with intralesional methylene blue in HS lesions.

METHODS

A retrospective cross-sectional study was performed. Forty-one patients were treated with intralesional methylene blue and a diode lamp. Follow-up was carried out at 1 and 6 months after therapy. Efficacy was determined by the diameter reduction of the lesion measured by high-frequency ultrasound.

RESULTS

A reduction of ≥75% in the maximum diameter was recorded in 58.5% of the lesions, while 22% showed a reduction between 50% and 75%, and 19.5% showed a reduction of <50%. Recurrence rate was 12.5%. The lesions treated in patients with typical forms of HS (Canoui-Poitrine phenotype I) had a better therapeutic response. No statistically significant differences were found in terms of lesion location or concomitant treatment.

CONCLUSION

This therapy may potentially be a cost-effective and well-tolerated local therapy for Hurley I-II patients with superficial abscesses and fistulas.

Synergistic effect of photodynamic treatment and doxorubicin on triple negative breast cancer cells

Breast cancer is a metastatic cancer that can spread to other organs, such as the bone, liver, and brain. There are many treatments for breast cancer, such as surgery and chemotherapy, but they lead to resistance and side effects. Therefore, the discovery of new therapies with high efficacy and low toxicity that selectively affect cancer cells is of great importance. Of late, the combination therapy has been suggested as a novel approach compared to existing treatments. In the present study, the effect of the combined treatment of doxorubicin (DOX) and methylene blue activated in the presence of laser irradiation (PDT) on triple-negative breast cancer cells has been investigated. Human breast cancer cell line MDA-MB-231 was exposed to different concentrations of DOX, methylene blue (MB) and DOX-methylene blue (MB-DOX) combination therapy in two different conditions: first the treatment with DOX and then with MB-PDT, and another treatment first with MB-PDT and then with DOX. Cell viability was evaluated using the MTT assay. Morphological and colonization changes were observed by light microscopy. The occurrence of apoptotic cell death was assessed by double-staining ethidium bromide-acridine orange using fluorescence microscopy and flow cytometry. The results showed that the combination of using MB-PDT, followed by DOX (even at low concentrations), has a better effect on inducing cancer cell death in comparison to DOX alone. The result of this study suggests that the combination therapy of MB-PDT-DOX can be used as a potential strategy for the treatment of triple-negative breast cancer cells.

Vulvar hidradenitis suppurativa: Clinical cross-sectional study of 25 patients

Hidradenitis suppurativa (HS) involving the vulva is seldom reported in the gynecological or dermatological literature. The aim of this study was to describe the clinical characteristics of HS with vulvar affectation (VHS) and to compare it with patients without vulvar involvement. A cross-sectional study was conducted in a tertiary academic referral centre in Spain from May 1, 2015 to October 1, 2019. This study included 230 women with HS diagnosed in our hospital, 25 of them had vulvar involvement. In order to clinically characterize patients, demographic factors, comorbidities, clinical features, prescribed treatments and complications were recorded. The VHS group presented later median age of onset and lower body mass index (BMI) (P = 0.048), they mainly belonged to latent class 2 (LC2) and LC3 phenotypes involving groins, perineal and pubic area. A higher incidence of psychiatric disease was found in VHS (32% vs 10.7%). Significant positive association with fistula (P < 0.001), LC2 phenotype (P = 0.014), acne (P = 0.021) and thyroid disease (P = 0.006), and negative association with axillar lesions (P = 0.001) were noted. Ultrasonographical study of vulvar lesions demonstrated that most of them were fistulas with high Doppler signal suggestive of high inflammatory load. In conclusion, VHS is mostly seen in women with later onset and lower BMI and higher incidence of psychiatric disease compared to those without vulvar involvement. It is clinically characterized by the presence of fistulas and barely absent axillary involvement. Early diagnosis and treatment could be essential to prevent complications and quality of life impairment.

Molecular interaction and cellular studies on combination photodynamic therapy with rutoside for melanoma A375 cancer cells: an in vitro study

Background

Melanoma as a type of skin cancer, is associated with a high mortality rate. Therefore, early diagnosis and efficient surgical treatment of this disease is very important. Photodynamic therapy (PDT) involves the activation of a photosensitizer by light at specific wavelength that interacts with oxygen and creates singlet oxygen molecules or reactive oxygen species (ROS), which can lead to tumor cell death. Furthermore, one of the main approches in the prevention and treatment of various cancers is plant compounds application. Phenolic compounds are essential class of natural antioxidants, which play crucial biological roles such as anticancer effects. It was previously suggested that flavonoid such as rutoside could acts as pro-oxidant or antioxidant. Hence, in this study, we aimed to investigate the effect of rutoside on the combination therapy with methylene blue (MB) assisted by photodynamic treatment (PDT) using red light source (660 nm; power density: 30 mW/cm²) on A375 human melanoma cancer cells.

Methods

For this purpose, the A375 human melanoma cancer cell lines were treated by MB-PDT and rutoside. Clonogenic cell survival, MTT assay, and cell death mechanisms were also determined after performing the treatment. Subsequently, after the rutoside treatment and photodynamic therapy (PDT), cell cycle and intracellular reactive oxygen species (ROS) generation were measured.

Results

The obtained results showed that, MB-PDT and rutoside had better cytotoxic and antiprolifrative effects on A375 melanoma cancer cells compared to each free drug, whereas the cytotoxic effect on HDF human dermal fibroblast cell was not significant. MB-PDT and rutoside combination induced apoptosis and cell cycle arrest in the human melanoma cancer cell line. Intracellular ROS increased in A375 cancer cell line after the treatment with MB-PDT and rutoside.

Conclusion

The results suggest that, MB-PDT and rutoside could be considered as novel approaches as the combination treatment of melanoma cancer.

Investigation of LED-based photodynamic therapy efficiency on breast cancer cells

Photodynamic therapy (PDT) is based on special light source, photosensitizer (PS), and in the presence of oxygen. Different light sources have been used for PDT applications. Recent studies have focused on LED light sources for PDT applications due to reducing the cost of laser-based PDT and providing easy access for research laboratory or clinic facilities. LED-mediated PDT applications have shown promising results for the treatment of different types of disease. However, few studies have determined the effects of LED-based PDT on cancer cells. For the first time, the aim of this study was to explore the therapeutic effects of 5-aminolevulinic acid (5-ALA)-mediated PDT after LED irradiation on two sub-types (a poorly aggressive MCF-7 and a highly aggressive MDA-MB-231) of breast cancer cell lines. The effectiveness of 5-ALA PDT treatment was evaluated by WST-1, annexin V, and acridine orange staining with different energy levels. The LED system was specially developed with optical power and wavelength stability techniques. The system consists of user interface and embedded LED controller with real-time optic power output calibration by photodiode feedback. Our results demonstrated that the cell viability of breast cancer cells was considerably decreased a LED dose-dependent manner (P < 0.05). Additionally, a significant increase in the percentage of apoptotic cells was detected in breast cancer cells after irradiation with LED at a density of 18 and 30 J/cm² energy. Consequently, the LED system could be effectively used for irradiation of 5-ALA in the treatment of breast cancer cells.

Medical and Surgical Management of Hidradenitis Suppurativa: A Review of International Treatment Guidelines and Implementation in General Dermatology Practice

BACKGROUND

Hidradenitis suppurativa (HS) is a chronic painful skin disease that severely impairs patients' quality of life. While high-quality trials of HS therapies remain limited, medical knowledge of best treatment practices is rapidly evolving, leading to the recent publication of multiple international treatment guidelines for HS.

SUMMARY

This review compares international HS treatment guidelines, describes evidence for effectiveness of common and emerging HS therapies, and provides guidance for integrating evidence-based HS care into practice. Although over 50 medical and procedural treatments are mentioned across international HS guidelines, only adalimumab and infliximab have grade B/weak recommendation or higher across all major guidelines. This review describes the appropriate patient selection and effectiveness of the most commonly used medical and procedural treatments for HS. It also includes recommendations for counseling, dosing, and duration of medical therapies as well as procedure videos for the practicing dermatologist.

Emerging medical treatments for hidradenitis suppurativa

Hidradenitis suppurativa (HS) is a chronic inflammatory disease affecting intertriginous skin areas, and it is characterized by recurrent painful episodes of inflammatory drainage. Although the pathophysiology of HS is not fully understood, recent research points to an imbalance of cytokines as a contributing factor to the associated symptoms of purulent drainage and sinus tract formation. HS lesions are often characterized by a superimposed pathogenic/commensal bacterial infection that can improve with targeted antibiotic therapy. New medical treatments have emerged in recent years, many of which specifically work against a variety of proinflammatory mediators associated with HS. These newer, specified treatment options, in conjunction with surgery and lasers, are thought to provide positive outcomes and an overall improvement in quality of life in patients with HS.

Laser and Light-Based Treatment Modalities for the Management of Hidradenitis Suppurativa

Hidradenitis suppurativa is a chronic inflammatory skin disease characterized by inflammatory nodules, abscesses, and sinus tracts in intertriginous areas that has a significant impact on patient quality of life. Treatments range from topical, intralesional, systemic, and surgical. Furthermore, laser and light-based treatment options have become increasingly popular because of the limitations of adverse effects associated with systemic therapy and decreased down-time associated with laser and light therapy. These modalities are thought to work through a variety of mechanisms including decreasing inflammation, destroying hair follicles, targeting sebaceous glands, killing bacteria, and debulking lesions through ablation. This review explores these laser and light-based treatment modalities for the treatment of hidradenitis suppurativa.

North American clinical management guidelines for hidradenitis suppurativa: A publication from the United States and Canadian Hidradenitis Suppurativa Foundations: Part I: Diagnosis, evaluation, and the use of complementary and procedural management

Hidradenitis suppurativa is a chronic inflammatory disorder affecting hair follicles, with profoundly negative impact on patient quality of life. Evidence informing ideal evaluation and management of patients with hidradenitis suppurativa is still sparse in many areas, but it has grown substantially in the last decade. Part I of this evidence-based guideline is presented to support health care practitioners as they select optimal management strategies, including diagnostic testing, comorbidity screening, and both complementary and procedural treatment options. Recommendations and evidence grading based on the evidence available at the time of the review are provided.

Treating hidradenitis suppurativa with photodynamic therapy

Hidradenitis suppurativa is a chronic, recurring, and disabling inflammatory condition of the skin. There is no cure for hidradenitis suppurativa and treatment must be adapted to each individual patient. Several studies have been published since 2004 on the use of photodynamic therapy to treat hidradenitis suppurativa. The use of superficial or interstitial illumination with 5-amino-levulinic acid (5-ALA) or methylene blue (MB) have been proposed. Injecting 5-ALA or MB followed by illumination with a fiber optic sensor placed inside the lesion appears to be a better method of treating these thick lesions.

An update on the pathogenesis of hidradenitis suppurativa: implications for therapy

INTRODUCTION

Hidradenitis suppurativa is a chronic, inflammatory disease characterized by painful nodules, abscesses, and sinuses in the intertriginous areas, with significant associated comorbidities. The pathogenesis remains unclear, although advances have been made in understanding the disease process. Management of the disease is challenging, with a wide range of treatment options available with variable clinical response. Areas covered: This review discusses the most updated studies on the complex pathogenic mechanisms of hidradenitis suppurativa and the relevant literature on the current treatment options for this condition. Expert commentary: There is increasing evidence supporting the role of Th17 cells and enhanced expression of IL-17 and IL-1β, which represent potential targets for therapy. Bacteria and biofilms are likely contributory but secondary drivers of inflammation. There is also evolving evidence to suggest the presence of systemic comorbidities associated with HS, which underlie the importance of better understanding the pathogenesis and treatment of this disease.

Intralesional Diode Laser 1064 nm for the Treatment of Hidradenitis Suppurativa: A Report of Twenty Patients

AIM

Hidradenitis suppurativa (HS) is a chronic inflammatory disease, commonly characterized by painful, deep dermal abscesses and chronic draining sinus tracts. Recently, laser and light-based therapies have become more commonly used in the management of HS.

MATERIAL AND METHODS

We report 20 HS patients treated with a 1064 nm wavelength, emitted from a diode laser, launched in an optical fibre through intracavitary modalities.

RESULTS

Each patient underwent four laser sessions, one every two weeks. we recorded a significative reduction (31%) of Sartorius score from 28.55 ± 13.04 to 19.75 ± 12.29 after 4 laser sessions (p < 0.05). No one has had a worsening of the disease.

CONCLUSION

Intralesional diode laser 1064 nm can be a good treatment option for patients with moderate and localized hidradenitis suppurativa, because it is minimally invasive, doesn't have significant complications and provides a rapid post-treatment recovery.

Photodynamic Therapy and Skin Appendage Disorders: A Review

Photodynamic therapy (PDT) is a noninvasive treatment that utilizes light treatment along with application of a photosensitizing agent. In dermatology, PDT is commonly used and approved for the treatment of oncological conditions such as actinic keratosis, Bowen disease and superficial basal cell carcinoma. In the last 2 decades however, PDT has also been used for the treatment of several nonneoplastic dermatological diseases. The present review summarizes published data on PDT application in skin appendage disorders. Our literature review shows that: (a) PDT may be a suitable treatment for acne, folliculitis decalvans, hidradenitis suppurativa, nail diseases, and sebaceous hyperplasia; (b) there is a lack of agreement on PDT features (type, concentrations and incubation period of used substances, number and frequency of PDT sessions, optimal parameters of light sources, and patient characteristics [e.g., failure to previous treatments, disease severity, body surface area involved, etc.] which should guide PDT use in these diseases);