Wood's lamp uses long-wave UV radiation to cause tissues to fluoresce, allowing diseases and conditions to be diagnosed. It emits radiation between 320-400nm, causing fluorophores in the skin like collagen to glow blue. Various conditions have distinctive fluorescence - vitiligo appears bright blue due to lack of melanin, while pityriasis versicolor glows yellow-gold due to a skin yeast. Wood's lamp is useful for diagnosing infections caused by fungi, bacteria, and viruses based on the fluorescent compounds they produce. It can also detect pre-cancerous and cancerous lesions treated with fluorescent precursors.

1. By /Azza Samy

2. Introduction
 A diagnostic method must be easy and quick to
perform while delivering an accurate and
consistent result.
 An example of a diagnostic tool that meets these
criteria is the Wood’s lamp.

4. Wood’s light physics
 Wood’s lamp’s long-wave UV radiation (UVR)
emission is generated by a high-pressure mercury arc
fitted with a compounded filter made of barium
silicate with 9% nickel oxide, the so-called
‘‘Wood’s filter.’’
 This filter is opaque to all light except for a band
between 320 and 400 nm with a peak at 365 nm.

5. Wood’s light physics(cont.)

6. Wood’s light physics(cont.)
 A photon hitting the skin can be reflected away
from the skin, scattered deeper into the skin, or
absorbed by a molecule.
 Fluorescence of tissue occurs when light of shorter
wavelengths, in this case 340–400 nm, initially
emitted by Wood’s light, is absorbed and radiation
of longer wavelengths, usually visible light, is
emitted.

7. Wood’s light physics(cont.)
 The skin contains a plethora of fluorescent
compounds, such as collagen, elastin, coenzymes and
many others, which respond notably to UVA light.
 If the skin is intact and not influenced by diseases
or external factors: one can observe a bluish
fluorescence due to these fluorophores.

8. Wood’s light physics(cont.)
 In vitiligo, for example,diagnosis is confirmed by the
lack of absorption by melanin residing in melanocytes
or keratinocytes, resulting in bright bluish-white
patches.
 An exception is porphyria, in which there is an excess
of fluorescent compounds in the skin, or skin
infections caused by certain fungal or bacterial
microorganisms that produce fluorescent chemicals.

9. Technique
 Ideally, the lamp should be allowed to warm up for
about 1 min.
 Black occlusive shades or a windowless room are
preferred.
 It is also essential that the examiner becomes
dark-adapted in order to see the contrasts clearly.
 The lamp is held about 10-30cm from the lesion.

10. Considerations
 Do not wash before the test, because that may cause a
false-negative result.
 Other materials may also glow. For example, some
deodorants, make-ups, soaps, and even lint may be
visible with the Wood's lamp.
 Not all infections can be detected with the light. Some
species of fungi and bacteria do not contain
fluorescent chemicals

11. Practical applications

12. Practical applications
(Pigment disorders)
 In hypopigmented or depigmented lesions,
 There is less or no epidermal melanin. Consequently,
there is a window through which the Wood’s light-
induced autofluorescence of dermal collagen can be
seen.
The lesions appear bright blue–white due to
autofluorescence.

13. Pigment disorders(cont.)
 In hyperpigmented lesions,
When incident light impinges upon the skin, photons
of shorter wavelengths, especially UVB (290–320 nm)
and UVA (320–400 nm), are more easily scattered by
the stratum corneum and the epidermis.
 Contrarily, photons of longer wavelengths, such as the
visible range (400–800 nm), penetrate more deeply
into the dermis.

14. Pigment disorders(cont.)
Melanin absorbs light very strongly in both the UV and
visible regions.
When Wood’s light is illuminated over a heavily
melanized epidermis, most of its output is absorbed,
while the less darkly pigmented adjacent skin scatters
and reflects light as usual, resulting in enhanced
contrasts at the border zone between areas of differing
melanization.

15. Pigment disorders(cont.)
 Variations in epidermal pigmentation thus become
more apparent under Wood’s light than under
ordinary room light.
 For dermal pigmentation, this contrast is less apparent
under Wood’s light because some of the
autofluorescence of the dermal collagen takes place
both above and below the dermal melanin, which
serves to diminish the amount of fluorescence
returned to the eyes.

16. Melasma
 Melasma is a common hyperpigmentary disorder
of the skin caused by an overproduction of
pigment on sun exposed areas, mainly the face,
which results in hyperpigmented patches.
 In melasma, the hyperpigmentation can be
epidermal, dermal or mixed.
 Melasma is treated with depigmenting creams or
with other methods such as laser and IPL therapy.

17. Melasma(cont.)
 In this treatment, mainly the epidermal pigment
responds.
 The Wood’s lamp is not only beneficial to confirm
diagnosis; in addition, it can distinguish whether
the hyperpigmentation is epidermal, dermal or
mixed and there by determine whether therapy is
effective or not.

18.  Epidermal-type melasma shows enhancement of color
contrast when examined under Wood’s light as
compared to visible light.
 Conversely, melasma of dermal type, which may have a
slight bluish hue in natural sunlight, does not
demonstrate such contrast enhancement when
seen under Wood’s light.

19.  Patients with mixed-type melasma showed color
enhancement in some areas, but not in others.
 Melasma in patients with darker complexions (skin
types V and VI) was more evident in visible light than
under UV light, hence the Wood’s light inapparent
type.

21. Comparison between photography with visible light (top) and with
the use of Wood's lamp (bottom) highlighting the limits of the
frontal macules of melasma .

22. Vitiligo
 Vitiligo is a disease in which skin and hair lose their
melanocytes resulting in depigmented patches on the
skin,varying in size and shape.
 The Wood’s lamp can be used to confirm diagnosis
when vitiligo is suspected. Furthermore, it allows to
distinguish vitiligo from an anaemic naevus, pityriasis
versicolor and pityriasis alba.

23.  In vitiligo, because of loss of epidermal melanin,
depigmented patches appear bright bluish-white with
sharp demarcations in the Wood’s light.
 In contrast, an anaemic naevus, caused by local dermal
vasoconstriction with normal overlying epidermal
pigment, does not show up in the Wood’s light.

24.  In pityriasis versicolor, the yeast causing the skin
disorder gives a yellowgold fluorescence.
 Finally, pityriasis alba, with irregular parakeratosis and
little melanocyte activity, is not noticed in the Wood’s
light.
 Follicular repigmentation following oral
photochemotherapy can be demonstrated earliest by
the use of Wood’s light.

25. Vitiligo: bright bluish-white fluorescence in Wood’s light.

26. Progressive macular hypomelanosis
 PMH is a pigment disorder with non-itching, non-
scaly, hypopigmented macules, mainly localized on
the trunk.
 Westerhof found a relation between PMH and
Propionbacterium acnes.

27. Progressive macular hypomelanosis
(cont.)
 Examination of PMH with the Wood’s lamp showed
bright bluish-white fluorescence of the skin lesions
due to the lack of melanin, as well as follicle-bound
coral-red fluorescence due to coproporfyrine III.
 Coproporfyrine III is a chromophore produced by
Propionbacterium acnes

28. Progressive macular hypomelanosis
(cont.)
Progressive macular hypomelanosis: bright bluish-white lesions
and follicle-bound coral-red fluorescence.

29. Tuberous sclerosis
 An ‘ash-leaf’ macule is a leaf-shaped, hypopigmented
macule, a characteristic of tuberous sclerosis.
 On a light skin type, this lesion can be hard to see but
easily detected with the Wood’s lamp.
 Finding these lesions early on allows dermatologists to
alert primary care physicians as to possible seizures or
other clinical problems.

30. Tuberous sclerosis(cont.)
An ‘ash-leaf’ macule easily detected with the Wood’s
lamp.

31. Infections of the skin
((Fungi and yeasts
 Fungi and yeasts cause dermatomycoses of skin,
hair and nails. Fungi are divided into three
different strains, Microspora, Trichophyton and
Epidermophyte species.
 The Microspora species produce a metabolite,
pteridine, which fluoresces bright-green if
illuminated by the Wood’s lamp .

32. Tinea capitis
 Tinea capitis is a trichomycosis often caused by
Microspora species.
 When tinea capitis is suspected, the diagnosis can be
directly confirmed using the Wood’s lamp .
 However, tinea capitis can also be caused by
a Trichophyton species, which does not fluoresce. That
is why a lack of fluorescence can never exclude tinea
capitis.

33. Tinea capitis(cont.)
 One exception in the Trichophyton species,
Trichophyton schoenleinii the cause of favus,
causes yellowish, cup-shaped crusts, grouped in
patches like a piece of honeycomb. In the Wood’s
light, it causes a blue fluorescence.

34. Tinea capitis caused by Microsporum: bright-green fluorescence.

35. Tinea manuum: bright-green fluorescence in Wood’s light.

36. Pityriasis versicolor
 Pityriasis versicolor is a superficial fungal infection
of the skin caused by Malassezia furfur, a spore-
forming yeast.
 Infected lesions fluoresce yellow-gold, also
described as chamois leather.

37. p. versicolor under Wood's lamp

38. Pityrosporum folliculitis
 Pityrosporum folliculitis is caused by the same yeast as
pityriasis versicolor and is therefore also seen as its
local or follicular form.
 Overgrowth of Malassezia furfur causes follicular
erythematous papules and pustules, sometimes
itching and mainly localized on chest and upper back.
 When illuminated by the Wood’s light, a follicular
pattern of bluish-white fluorescence is seen, which
allows for a clear distinction between pityrosporum
folliculitis and a bacterial folliculitis.

39. Bacterial infections
((Propionbacterium acnes
 Propionbacterium acnes produces coproporphyrin
III and protoporphyrin IX, in the Wood’s light these
chromophores show an orange-red fluorescence.
 On the facial skin, the Wood’s lamp highlights an
orange-red fluorescence from comedones.

40. Propionbacterium acnes in comedones: follicle-
bound coral-red fluorescence.

41. Pseudomonas infection
 The Wood’s lamp can also be used to detect
Pseudomonas infections of the skin, for example,
in burns or toe web infections.
 Pseudomonas bacteria excrete a pigment,
pyoverdin, which fluoresces yellowish-green in the
Wood’s light.

42. Pseudomonas infection(cont.)
 The Wood’s lamp can be used as an early
diagnostic tool to detect Pseudomonas
infection of burns or other wounds, long
before Pseudomonas shows up in a bacterial
culture, allowing to start the right treatment
at an early stage.

43. Pseudomonas infection: yellow-green fluorescence
in Wood’s light.

44. Erythrasma
 Erythrasma is a skin infection caused by overgrowth
of Corynebacterium minutissimum.
 It occurs in body folds and causes a scaly, red-brown
discoloration of the skin and an itching or burning
sensation.

45. Erythrasma(cont.)
 Corynebacterium minutissimum produces
coproprophyrine III, which causes a coral-red
fluorescence when illuminated by Wood’s light.
 Because of the coralred fluorescence, the Wood’s
lamp is a direct diagnostic tool to distinguish
erythrasma from intertrigo, tinea inguinalis or
psoriasis inversa.

46. Erythrasma: coral-red fluorescence in Wood’s light.

47. Porphyria
 Porphyria is a metabolic disorder caused by an
enzymatic disturbance in the biosynthesis of
haem.
 Because of a lack of haem, porphyrins accumulate.
 Due to an excess of porphyrin metabolites,
sensitivity to light occurs, which can manifest
clinically in various forms.

48. Porphyria(cont.)
 Porphyrin fluoresces pink-red in the
Wood’s light.
 Depending on the type of porphyria,
accumulation can be noted in urine, faeces,
erythrocytes or teeth.

49. Characteristic fluorescence observed in the principal
porphyrias

50. congenital erythropoietic porphyria - teeth: red on
woods lamp

51. Porphyria Cutanea Tarda: urine flouresces pink red

52. Tumours (Photodynamic diagnosis)
 Based on the fact that δ-ALA-derived porphyrins
preferentially accumulate in neoplastic tissues,
Fritsch et al. reported the use of topical δ-ALA and
Wood’s lamp to delineate the margin of recurrent
basal cell carcinomas.
 20% ALA ointment was applied to the tumor and
left on for 4–6 h under occlusion allowing
protoporphyrinogen IX to accumulate, after which
the area was illuminated withWood’s light.

53. Tumours (Photodynamic
diagnosis)
 The tumor emitted bright-red fluorescence.
 These fluorescence positive areas proved to be
basal cell carcinomas on histologic examination.
 This photodynamic diagnosis has proved useful in
other conditions, including solar keratosis,
Bowen’s disease, squamous cell carcinoma, and
extramammary Paget’s disease.

54. Tumours (Photodynamic diagnosis)
 This technique, when perfected, will be of great
help to physicians taking care of skin cancers.
 It seems likely that additional specific,
noninvasive, and useful optical techniques will be
developed in the next decade.

56. THANK YOU