Dermoscopy and UV light – what’s it all about?
In the last year or two we have seen a new addition to dermatoscopes – the inclusion of UV light illumination. This article examines its rise, utility and looks at potential applications in podiatry.
Ultraviolet (UV) Light History
Ultraviolet (UV) light is a type of invisible electromagnetic radiation with wavelengths shorter than visible light, ranging from 100 to 400 nanometres (nm).
UVA (315–400 nm): The longest wavelength; penetrates deep into the skin and causes tanning and aging.
UVB (280–315 nm) Medium wavelength; triggers vitamin D production in the skin but causes sunburn.
UVC (100–280 nm): The shortest and most energetic wavelength; kills bacteria and viruses but is blocked by the ozone layer.
The concept of using UV light for skin assessment is not new – it dates back to around 1903 with the invention of the Woods lamp [1]. It was noted then how certain chemicals produce fluorescence when exposed to UV light. For many years the Woods lamp has been employed in clinical practice – covered previously in my blog here. The UV emitted in these devices is longer wave (around 365nm - 385nm) and at low power so there are no harmful UVC and UVB rays and the energy levels used produce no cellular changes.
Fluorescence under UV light is due to a phenomenon called Stokes Shift. Molecules rapidly absorb UV wavelength photons increasing their level of excitation. This energy is then partly dissipated through vibration and heat before photons are emitted as fluorescence. It was first documented by George Stokes in a paper in 1852 in the Philosophical Transactions of the Royal Society of London. In his original paper he noted that substances could absorb invisible UV and re-emit this as lower wavelength (visible) light [2].
Dermoscopy has some advantages over traditional Woods light in day-to-day practice. Firstly, magnification. Most dermatoscopes will magnify by a factor of ten increasing lesion visibility and clarity. In addition, the UV function does not need a darkened room to be utilised like Woods Light. Whilst the latter can scan a widespread area, the dermatoscope allows for more microstructural evaluation of lesions often pinpointing anatomical locations such as dermatoglyphics, sweat duct openings and hair follicles.
Pitted Keratolysis
In 2023, a paper describes how UV dermoscopy can be helpful in diagnosing Pitted Keratolysis [3]. The condition is a superficial bacterial infection of the stratum corneum. The bacteria (Kytococcus sendentarius and Corynebacterium) by action of its enzymes hydrolyses intercellular desmosomal attachments, degrading skin creating characteristics pits in the epidermis which often have a distinctive odour [4].
Interestingly, as the authors discovered under 385nm wavelength (UV) coproporphyrin 3 produced by the bacterium emits a coral pink discolouration. Examination of the dermatoscopic images highlighted a parallel ridge fluorescence.
UV Dermoscopy and Fungal Infection
Despite many claims, most pathogenic fungi, particularly those found commonly on the foot, do not fluoresce under UV light. Data suggests that only one or two, less common dermatophytes will fluoresce. These include species of the Microsporum (canis, audouuinii, ferrugineum, distortum) and Trichophyton schoenleinii, most of which are observed in tinea capitis and occasionally tinea corporis. This is due to a metabolite call pteridine [5]. Rarer, non-dermatophytes Phaeoacremonium [6] and Malassezia [7] have also been noted to fluoresce under laboratory conditions. As Woods light experiments demonstrate the common dermatophytes found on the feet do not produce any fluorescence under UV light.
UV Dermoscopy and Scabies
The use of standard polarised dermoscopy for diagnosis of scabies has been well documented for many years [8, 9]. Dermatoscopic evaluation of burrows revealed a triangular shape at the base of the burrow corresponding to the headpiece and fore legs of the mite, coined the “Delta-wing sign”. The inclusion of UV evaluation has added new features. Firstly, a light blue, serpiginous (snake-like) tract corresponding to the mites burrow, particularly in darker skin tones [10].
Intertrigo / Pseudomonas
This is a topic I have covered in a previous article (Link here), but the condition is a complication of athlete’s foot. Mixed infection of the webspace can lead to inflammation and local tissue damage. Pseudomonas is a common bacterium involved in the infection and will produce a green fluorescence known as pyoverdin. Corynebacterium, as mentioned above, may also be present producing a coral red fluorescence due to the production of coproporphyrin 3.
The future of UV dermoscopy
From the early literature it is clear that UV element in dermoscopy has an application in skin assessment. UV devices have only been available for around 4 years or so and are slowly diffusing into dermatological practice, consequently new techniques and applications are yet to be reported. The first systematic review on this topic [11] was only published last year and highlights that research is at an early stage with further work required to uncover its full potential.
References
1. Gupta, L. and M. Singh, Woods Lamp. Indian Journal of Dermatology, Venereology and Leprology, 2004. 70(2): p. 131–135.
2. Stokes, G.G., On the change of refrangibility of light. Proceedings of the Royal Society of London, 1854(6): p. 195–200.
3. Pietkiewicz, P., et al., Ultraviolet-Induced Fluorescence Dermoscopy Reveals Fluorescent Clues in Pitted Keratolysis. Dermatology Practical & Conceptual, 2023. 13(3): p. e2023242.
4. Bristow, I.R. and Y.L.H. Lee, Pitted keratolysis: a clinical review. Journal of the American Podiatric Medical Association, 2014. 104: p. 177–182.
5. Wolf, F.T., E.A. Jones, and H.A. Nathan, Fluorescent Pigment of Microsporum. Nature, 1958. 182(4633): p. 475–476.
6. Elston, D.M., Fluorescence of fungi in superficial and deep fungal infections. BMC Microbiol, 2001. 1: p. 21.
7. Mayser, P., et al., Pityriacitrin – an ultraviolet-absorbing indole alkaloid from the yeast Malassezia furfur. Archives of Dermatological Research, 2002. 294(3): p. 131–134.
8. Zalaudek, I., et al., Entodermoscopy: A New Tool for Diagnosing Skin Infections and Infestations. Dermatology, 2007. 216(1): p. 14–23.
9. Argenziano, G., G. Fabbrocini, and M. Delfino, Epiluminescence Microscopy: A New Approach to In Vivo Detection of Sarcoptes scabiei. Archives of Dermatology, 1997. 133(6): p. 751–753.
10. Errichetti, E., et al., Dermoscopy of Scabies: Utility of Polarised and Ultraviolet-Induced Fluorescence Examination in Fair and Dark Skin. Australasian Journal of Dermatology, 2025. 66(2): p. 69–74.
11. Bhat, Y.J., M.S. Ul Islam, and E. Errichetti, Ultraviolet-Induced Fluorescence Dermoscopy, a Novel Diagnostic Technique in Dermatological Practice: A Systematic Review. Indian Dermatology Online Journal, 2025. 16(1).
