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Photodiagnosis and Photodynamic Therapy 46 (2024) 104089
Available online 16 April 2024
1572-1000/© 2024 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-
nc-nd/4.0/).
Identification of skin tumors margins using Wood’s light: “The umbrella effect” 
A R T I C L E I N F O 
Keywords 
Wood’s light 
Basal cell carcinoma 
Biopsy 
Dermoscopy 
Mohs 
Surgery 
Ultraviolet dermoscopy 
Wood’s light (320–450 nm, peak 365 nm) has recently been 
described for identification of biopsy site of basal cell carcinomas (BCC) 
[1], which appear as darker areas than the surrounding skin. The au-
thors suggest that this phenomenon may be explained by the inflam-
mation and hypervascularization of scar tissue secondary to the 
procedure. However, we found that non-biopsied BCC (Fig. 1a–d), as 
well as other tumors such as B cell follicular lymphoma (Fig. 1d, e), 
showed a similar image under Wood’s light (darker than the surround-
ing area), which could suggest that the lower fluorescence would not 
only be related to a recent scar, but also to the presence of tumor or 
tumor remnants after the biopsy. 
Normal skin has chromophores found in elastin (a crosslinking 
tricarboxylic amino acid with a pyridinium ring) and collagen (tyrosine) 
(2a, b) [2], which give normal skin a light purplish tone under the 
Wood’s light. However, BCC and other tumors have a darker appear-
ance. We believe this is because the neoplasm acts as an “umbrella” that 
is more opaque than normal skin to the UV light preventing it to easily 
reach the collagen and elastin of the dermis under the tumor (Fig. 2), 
and also precluding the fluorescence to reach the skin surface. This 
would also apply to recent scars, although, in our experience, they look 
slightly less dark than the tumor (Fig. 1f). In the case of old hypo-
pigmented scars (for example secondary to cryotherapy), they are seen 
as brighter areas than the surrounding skin (Fig. 1c, d). Moreover, this 
effect allowed us for better identification of the tumor margins in poorly 
demarcated BCC when planning Mohs surgery, without needing any 
photosensitizer [3]. 
Wood’s light has also been used for identification of the margins of 
lentigo maligna (LM) [4,5]. The darker appearance is believed to be 
related to a greater absorption of the UV light by the melanin, which is 
increased in these tumors. However, it came up to our attention that it 
also delimitates hypo or amelanotic areas of LM, such as the described 
by Atwan et al. [4] This could suggest that, at least in these areas, the 
darker appearance could also be because of the “umbrella” effect of the 
tumor, in addition to that of the melanin in pigmented areas. 
In conclusion, we believe that skin tumors obstruct the penetration of 
the UV light, making it difficult to reach the collagen and elastin 
underneath and, as a consequence, the fluorescence they could emit is 
also reduced. As a result, the tumor appears darker than the surrounding 
skin under Wood’s light examination, which we found very helpful to 
better delineate tumor margins prior to surgery. 
Funding 
None. 
The authors attest to obtaining written patient consent for the pub-
lication of recognizable patient photographs or other identifiable ma-
terial, with the understanding that this information may be publicly 
available. 
This study has not been previously published 
CRediT authorship contribution statement 
Pedro Gil-Pallares: Writing – review & editing, Writing – original 
draft, Visualization, Validation, Supervision, Software, Resources, 
Project administration, Methodology, Investigation, Formal analysis, 
Data curation, Conceptualization. Itziar Muelas-Rives: Writing – re-
view & editing, Writing – original draft, Visualization, Validation, Su-
pervision, Software, Resources, Project administration, Methodology, 
Investigation, Formal analysis, Data curation, Conceptualization. Alba 
Navarro-Bielsa: Writing – review & editing, Writing – original draft, 
Visualization, Validation, Supervision, Software, Resources, Project 
administration, Methodology, Investigation, Formal analysis, Data 
curation, Conceptualization. Yolanda Gilaberte: Writing – review & 
editing, Writing – original draft, Visualization, Validation, Supervision, 
Software, Resources, Project administration, Methodology, Investiga-
tion, Formal analysis, Data curation, Conceptualization. José Manuel 
Suárez-Peñaranda: Writing – review & editing, Writing – original draft, 
Visualization, Validation, Supervision, Software, Resources, Project 
administration, Methodology, Investigation, Formal analysis, Data 
curation, Conceptualization. 
Contents lists available at ScienceDirect 
Photodiagnosis and Photodynamic Therapy 
journal homepage: www.elsevier.com/locate/pdpdt 
https://doi.org/10.1016/j.pdpdt.2024.104089 
Received 30 March 2024; Received in revised form 13 April 2024; Accepted 15 April 2024 
www.sciencedirect.com/science/journal/15721000
https://www.elsevier.com/locate/pdpdt
https://doi.org/10.1016/j.pdpdt.2024.104089
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Photodiagnosis and Photodynamic Therapy 46 (2024) 104089
2
Fig. 1. (a) Dermoscopic image of basal cell carcinoma (BCC). (b) BCC as a darker area under Wood’s light (WL). (c) Clinical image of BCC recurrence (white arrows) 
and a hypopigmented scar of previous cryotherapy (star). (d) Under WL, compared to the surrounding skin, the BCC appears darker (white arrows), and the old 
cryotherapy scar brighter. (e) Clinical image of a follicular cutaneous B lymphoma (black arrow), and a scar of a previous punch biopsy (arrowhead). (d) Follicular 
cutaneous B lymphoma showing as a dark area (black arrow), and the recent scar from the biopsy has a subtle lighter tone (arrowhead). 
P. Gil-Pallares et al. 
Photodiagnosis and Photodynamic Therapy 46 (2024) 104089
3
Declaration of competing interest 
The authors declare no conflicts of interest. 
References 
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572–578, https://doi.org/10.1097/DSS.0000000000000345. 
Pedro Gil-Pallaresa,b,c, Itziar Muelas-Rivesa,b, Alba Navarro-Bielsaa,b,*, 
Yolanda Gilabertea,b, José Manuel Suárez-Peñarandac,d 
a Department of Dermatology, Miguel Servet University Hospital, Spain 
b IIS Aragón, Aragón, Spain 
c Universidad de Santiago de Compostela, Santiago de Compostela, Spain 
d Department of Pathology, Complejo Hospitalario Universitario de Santiago 
de Compostela,Santiago de Compostela, Spain 
* Corresponding author at: Department of Dermatology, Miguel Servet 
University Hospital, P.º de Isabel la Católica, 1-3, Zaragoza 50009, 
Spain. 
E-mail address: 582073@unizar.es (A. Navarro-Bielsa). 
Fig. 2. (a) (Masson’s trichrome x10) Basal cell carcinoma (BCC) in purple and collagen fibers in dermis stained in blue. The ultraviolet (UV) light is stopped by the 
BCC preventing it to reach the collagen underneath. (b) (Orcein x10) BCC in pink-red and elastic fibers in brown-black. (c) Structure of the skin, collagen in pink and 
elastin in brown, and a skin tumor in purple-blue. (d) Skin irradiated with Woods lamp. UV light is blocked by the tumor, but it easily penetrates the dermis of the 
surrounding tissue, where the fluorescence emitted by collagen and elastin reaches de skin surface. The potential low fluorescence that elastin and collagen under the 
tumor could emit is also stopped by the tumor. (e) The tumor is seen as a darker area in comparison with the surrounding normal skin that shows a light blue-purplish 
color, allowing for a more accurate delimitation of the tumor margins. 
P. Gil-Pallares et al. 
https://doi.org/10.1016/j.jaad.2023.05.089
https://doi.org/10.1016/j.jaad.2023.05.089
http://refhub.elsevier.com/S1572-1000(24)00127-3/sbref0002
http://refhub.elsevier.com/S1572-1000(24)00127-3/sbref0002
https://doi.org/10.1111/phpp.12166
https://doi.org/10.5826/dpc.1001a18
https://doi.org/10.5826/dpc.1001a18
https://doi.org/10.1097/DSS.0000000000000345
mailto:582073@unizar.es
	Identification of skin tumors margins using Wood’s light: “The umbrella effect”
	Funding
	CRediT authorship contribution statement
	Declaration of competing interest
	References