Dermatology: Practical and Conceptual Original Article | Dermatol Pract Concept. 2025;15(2):5466 1 Ultraviolet-induced Fluorescence Patterns in Psoriasis: Insights from a Large International Cohort Study Paweł Pietkiewicz1,2,3, Natalia Salwowska3,4, Verche Todorovska5, Marian Voloshynovych6, Paweł Falkowski3,7, Piotr Giedziun3,8, Cristian Navarrete-Dechent9, Adarsha Adhikari10, Nora Pollozhani11, Enzo Errichetti12 1 Centrum Medyczne Zwierzyniecka, Poznań, Poland 2 Unitelematica Leonardo Da Vinci, Zug, Switzerland 3 Polish Dermatoscopy Group, Poznań, Poland 4 Department of Dermatology, School of Medicine, Medical University of Silesia, Katowice, Poland 5 Dermatology Private Practice Skopje, North Macedonia 6 Department of Dermatology and Venereology, Ivano-Frankivsk National Medical University, Ivano-Frankivsk, Ukraine 7 Department of Family Medicine, Medical University of Białystok, Białystok, Poland 8 Faculty of Information and Communication Technology, Wrocław University of Science and Technology, Wrocław, Poland 9 Melanoma and Skin Cancer Unit, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 10 Medical Private Practice, Pokhara, Nepal 11 University Clinic of Dermatology, Ss Cyril and Methodius University of Skopje, Skopje, North Macedonia 12 Institute of Dermatology, Department of Medicine, University of Udine, Udine, Italy Key words: Psoriasis Diagnosis, Skin imaging, UVFD, Fluorescence Imaging, Protoporphyrin Citation: Pietkiewicz P, Salwowska N, Todorovska V, et al. Ultraviolet-induced Fluorescence Patterns in Psoriasis: Insights from a Large International Cohort Study. Dermatol Pract Concept. 2025;15(2):5466. DOI: https://doi.org/10.5826/dpc.1502a5466 Accepted: February 5, 2025; Published: April 2025 Copyright: ©2025 Pietkiewicz et al. This is an open-access article distributed under the terms of the Creative Commons Attribution- NonCommercial License (BY-NC-4.0), https://creativecommons.org/licenses/by-nc/4.0/, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original authors and source are credited. Funding: None. Competing Interests: None. Authorship: All authors have contributed significantly to this publication. Corresponding Author: Dr. Paweł Pietkiewicz. Centrum Medyczne Zwierzyniecka, Zwierzyniecka Street 30/28, 60-814 Poznań, Poland. ORCID ID: 0000-0001-7262-2456. E-mail: pietkiewicz.pp@gmail.com Introduction: Psoriasis is a common skin disease displaying a broad spectrum of clinical presentations that can sometimes pose diagnostic challenges. UV-induced fluorescence dermatoscopy (UVFD) is a novel dermatoscopy mode useful as a complementary diagnostic method in inflammatory dermato- ses. The understanding of red fluorescence in psoriasis, caused by protoporphyrin IX, in regard to clinical-morphological features, site-dependency, geographic variability, and bleaching with sun-exposure remains very limited. ABSTRACT 2 Original Article | Dermatol Pract Concept. 2025;15(2):5466 Introduction Psoriasis is a common skin disease displaying a broad spec- trum of clinical presentations that can sometimes pose diag- nostic challenges. Given its incidence across all age groups and its manifestation in cosmetically sensitive areas, the dis- ease imposes a significant psychological and socioeconomic burden on affected individuals worldwide. Dermatoscopy serves as a non-invasive auxiliary diagnostic tool that aids in the diagnostic process of common dermatoses, thereby im- proving diagnostic accuracy and clinician’s confidence [1–3]. Ultraviolet-induced fluorescence dermatoscopy (UVFD) is a novel dermatoscopic mode applicable to neoplastic, inflam- matory, infectious, and parasitic conditions [4–7]. This im- aging method utilizes the Stokes shift. In this phenomenon, ultraviolet (UV) light emitted by the diodes induces fluores- cence in the fluorophore (emission of light characterized by a longer wavelength and lower energy than the excitation light) [4]. A small portion of reflected UV light is filtered out by the dermatoscope UV filters, which allow only the visible light spectrum to pass through. A distinctive peripapillary red fluorescence exhibited under UVFD in certain psoriatic lesions is attributed to the accumulation of protoporphyrin IX in the stratum corneum, particularly in more severe cases [8,9]. The understanding of red fluorescence in psoriasis in regard to clinical-morphological features, site-dependency, geographic variability, and bleaching with sun exposure re- mains very limited. Moreover, it has been speculated that some fluorophores may either be washed away with water or diminish following sun exposure [4,9,10]. Objectives The study objective was to explore the patterns of UVFD in relation to demographic factors, psoriasis subtype, anatomical distribution of the lesions, Psoriasis Area and Se- verity Index (PASI) score, geographic region, seasonal varia- tions, and bathing practices on the day of examination. Methods In this retrospective international cohort study, performed between January 2023 and March 2024, we explored the patterns of UVFD in relation to the demographic fac- tors, psoriasis subtype, anatomical distribution of the lesions, Psoriasis Area and Severity Index (PASI) score, er- ythema, induration, and desquamation scores of particular lesions (0–3), geographic region (Central Europe: Poland, Ukraine; Southern Europe: Italy, North Macedonia), sea- sonal variations (winter, spring, summer, autumn), and bath- ing practices on the day of examination (yes/no). In the study group, we included patients diagnosed clinically and/or his- tologically with psoriasis who had received no targeted treat- ment for psoriasis in the six weeks before their examination and who did not have any overlapping dermatoses. A hybrid (conventional/UVFD) DL5 dermatoscope (DermLite; 3Gen, San Juan Capistrano, CA, USA) paired with a smartphone camera was used for dermatoscopic image acquisition. Clin- ical pictures were obtained with smartphone cameras. Cap- tured images were not proceeded/manipulated in any aspect. Statistical Analysis For the statistical analysis we have employed a series of Chi- squared tests for independence and independent samples t-tests with Python v3.12 (SciPy v1.11.3, seaborn v0.13.2). P<0.05 was considered statistically significant for all tests. All methods were carried out in accordance with relevant guidelines and regulations. Ethical approval was waived by the Ethics Committee of Ethics Committee of the Ivano- Frankivsk National Medical University (No 145/24), Objective: The study objective was to explore fluorescence patterns in relation to demographic and geographic factors, disease subtype, lesion morphology, Psoriasis Area and Severity Index (PASI) score, seasonal variations, and bathing practices. Method: This study included 356 UVFD images from 111 psoriatic patients naive to the treatment from Central and Southern Europe and explored fluorescence patterns in relation to demographic and geographic factors, disease subtype, lesion morphology, Psoriasis Area and Severity Index (PASI) score, seasonal variations, and bathing practices. For the statistical analysis we have employed a series of Chi-squared tests for independence and independent samples t-tests. Results: Red fluorescence was predominantly observed in subtypes affecting sun-protected areas in patients with higher PASI scores, especially erythema and induration. Geographic and seasonal vari- ability was observed, while age, sex, and bathing practices did not significantly affect fluorescence patterns. Conclusion: The study confirms that red fluorescence in psoriatic lesions under UVFD is suppressed by sun exposure and correlates with disease severity. Original Article | Dermatol Pract Concept. 2025;15(2):5466 3 Results A total of 111 patients (74 males, 37 females; mean age 49.75 years) contributed 356 photographs (mean, 3.21 pho- tos per patient). The results are presented in Table 1. In our study group, we found no correlation between red fluores- cence and age (P=0.603) or sex (P=0.247). Psoriatic sub- types exhibiting red fluorescence more frequently included inverse, follicular, guttate, and plaque psoriasis (P=0.006), with a notable reduction in frequency in palmoplantar variants (Figure 1A-I). Red fluorescence under UVFD was Ethics Committee of the Medical University of Białystok (APK.002.403.2024) and Ethics Committee of the Ss Cyril and Methodius University of Skopje (03.5505/2).The in- formed consent to publication form was signed by the pa- tients whose images are included in this study and/or their legal guardian(s). The data underlying this article are avail- able at Harvard Dataverse at https://dataverse.harvard.edu/ api/access/datafile/10126337 The authors used generative AI (ChatGPT 4o) to im- prove readability and language. All the authors reviewed the manuscript and take full responsibility for its contents. Table 1. Demographic and Clinical Data of 356 Psoriatic Lesions Analyzed for the Presence of Red Fluorescence Under UV-Induced Fluorescence Dermatoscopy. Psoriasis Cases (n=111) Demographics P Mean age (years) 49.75 0.603* M/F ratio 2.0 0.247* Geographic region Red fluorescence %red PYes No Central Europe 128 74 63.37 0.022** Southern Europe 78 76 50.65 PASI Red fluorescence %red PYes No <5 35 43 44.87 0.005* 5-10 68 55 55.28 >10 103 52 66.45 Site Red fluorescence %red Fluorescence frequencyYes No Thigh 31 5 86.11 High (≥66.67%) Buttock 11 2 84.62 Armpit 3 1 75.00 Groin 3 1 75.00 Intergluteal fold 8 3 72.73 Trunk 61 25 70.93 Genital area 10 5 66.67 Forearm 16 10 61.54 Medium (33.34-66.66%) Lower leg 35 22 61.40 Feet (dorsum) 2 2 50.00 Upper arm 15 21 41.67 Head & neck 1 3 25.00 Low (≤33.33%) Feet (sole) 1 4 20.00 Scalp 5 20 20.00 Face 1 6 14.29 Hand (dorsum) 2 12 14.29 Hand (palm) 1 8 11.11 Table 1 continues 4 Original Article | Dermatol Pract Concept. 2025;15(2):5466 Clinical subtypes Red fluorescence %red PYes No Inverse 23 9 71.88 0.006** Follicular 5 2 71.43 Guttate 38 21 64.41 Plaque 138 105 56.79 PP 2 12 14.29 PP pustular 0 1 0.00 Season Red fluorescence %red PYes No Spring 66 38 63.46 0.004** Summer 23 37 38.33 Autumn 20 19 51.28 Winter 97 56 63.40 Bathing on the day of the examination Red fluorescence %red PYes No No 186 132 58.49 0.605** Yes 20 18 52.63 %red – percentage of lesions exhibiting red fluorescence under ultraviolet fluorescence dermatoscopy * Independent sample t-test, ** Chi-squared for independence. Abbreviations: F: female; M: male; n: number of patients; PASI: psoriasis activity score index; P: statistical; significance; PP: palmoplantar Table 1. Demographic and Clinical Data of 356 Psoriatic Lesions Analyzed for the Presence of Red Fluorescence Under UV-Induced Fluorescence Dermatoscopy. (continued) associated with higher PASI scores (P=0.005) and correlated with erythema (P=0.008) and induration (P=0.034), but not desquamation (P=0.752) intensity in photographed psoriatic lesions. A significant geographic variability in the red fluo- rescence of psoriatic lesions was observed between Central and Southern Europe (P=0.022), with the winter and spring months showing a higher frequency of this phenomenon (P=0.004). Red fluorescence in psoriasis was predominantly observed on thighs, buttocks, armpits, groin, intergluteal folds, trunk, and genital areas. Bathing practices on the day of examination in psoriasis did not affect the UVFD pattern significantly (P=0.605) (Figure 1J-M). Discussion We have confirmed that red fluorescence under UVFD was associated with higher PASI scores [8], which is in line with a previously reported correlation between excited fluores- cence under Wood’s lamp and disease severity [11]. In our study, we have demonstrated that erythema and indura- tion are the key contributing factors. We hypothesize that vasodilation, inflammation, and papillomatosis may play crucial roles in the deposition of protoporphyrin IX within the stratum corneum and may influence UVFD findings. We believe that UVFD can be used as an auxiliary tool in erythematous psoriatic plaques without scales to rule out clinical differential diagnoses. It is still unclear whether the treatment modalities reducing induration or erythema could affect the UVFD fluorescence patterns. We posit that geo- graphic, seasonal, and anatomic variabilities of excited red fluorescence can be explained by the influence of sunlight on reducing protoporphyrin IX fluorescence in areas exposed to sunlight, particularly during sunny months and in warmer geographic regions (lighter clothing and outdoor activities). Speculatively, the lack of red fluorescence on the scalp ob- served in our study group may be related to the presence of Malassezia spp., given that the fungus exhibits enzymatic ac- tivity that suppresses porphyrin production in various clin- ical contexts, leading to the formation of “blackout areas” observed in pityriasis versicolor and seborrheic dermatitis [4,5]. In patients assessed with UVFD, taking a detailed his- tory concerning bathing and application of drugs/cosmetics may hugely affect the interpretation of the observed fluores- cence patterns [4]. Conversely to Corynebacterium-related red fluorescence of porphyrins in erythrasma and pitted ker- atolysis [4,10], patterns of excited red fluorescence in psori- atic plaques in our study were not significantly affected by bathing practices. The observed differences may be related to spatial distribution of the fluorophores. In erythrasma and pitted keratolysis, porphyrins are present on the surface of Original Article | Dermatol Pract Concept. 2025;15(2):5466 5 Figure 1. (A) Plaque psoriasis: trunk lesion (sun-protected area), clinical presentation. (B) Non-contact polarized der- matoscopy showing diffuse white scales. (C) Non-contact ultraviolet-induced fluorescence dermatoscopy (UVFD) displaying red protoporphyrin IX fluorescence. (D) Hand dorsum lesions (sun-exposed area), clinical presentation. (d); (E) Non-contact polarized dermatoscopy exhibiting diffuse white scales. (F) UVFD shows only bright blue fluo- rescence of keratin. (G) Palmoplantar psoriasis: hyperkeratotic plaques located on both palms, clinical presentation. (H) Non-contact polarized dermatoscopy exhibiting diffuse yellowish white scales. (J) UVFD displays only bright blue fluorescence. Psoriatic plaques: clinical presentation before washing. (K) UVFD presentation displaying red excited fluorescence of protoporphyrin IX and bright blue fluorescence of keratin. (L) Clinical presentation after washing with soap. (M) UVFD presentation shows retained red fluorescence. the epidermis and thus can be easily removed with bathing, whereas in psoriasis they can be detected in the stratum cor- neum [12]. Conclusions In this study we have demonstrated a correlation between sun exposure and the photo-bleaching of red fluorescence in psoriatic lesions, particularly noting that lesions in sun- protected areas more frequently display red fluorescence pat- terns under UVFD. The observed seasonal and geographic variability further substantiates this relationship. Our find- ings confirm that red fluorescence pairs with disease severity, as evidenced by higher erythema and induration scores of the assessed lesions. Moreover, we have shown that bathing practices do not influence the fluorescence patterns observed in psoriasis. We believe that our research contributes to a deeper understanding of the patterns of red fluorescence un- der UVFD in psoriasis. Ethical Approval was waived by the Ethics Committee of the Ivano-Frankivsk National Medical University (No 145/24), Ethics Committee of the Medical University of Białystok (APK.002.403.2024) and Ethics Committee of the Ss Cyril and Methodius University of Skopje (03.5505/2). The Consent to Publication form was signed by the patients included in this study. 6 Original Article | Dermatol Pract Concept. 2025;15(2):5466 7. Errichetti E, Plozner N, Enechukwu NA, et al. 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