WOOD LAMP SKIN EXAMINATION, SKIN DISEASE DETECTION, BLB, BLACK LIGHT BLUE LAMP

Description

What is
Wood lamp
skin examination?
Wood lamp examination is a diagnostic test in which the skin or
hair
is examined while exposed to the black light emitted by Wood lamp. Blacklight is invisible to the naked eye because it is in the ultraviolet spectrum, with a wavelength just shorter than the colour violet. The lamp glows violet in a dark environment because it also emits some light in the violet part of the electromagnetic spectrum.
What is a Wood lamp?
A traditional Wood lamp is a low-output mercury arc covered by a Wood filter (barium silicate and 9% nickel oxide) and emits wavelength 320–450 nm (peak 365 nm). The lamp was invented in 1903 by a Baltimore physicist, Robert W. Wood.
Modern black light sources may be specially designed BLB fluorescent lamps, mercury vapour lamps, light-emitting diodes, or incandescent lamps. Fluorescent black light tubes have a dark blue filter coating on the tube, which filters out most visible light. There are several models with varying properties. The medical Wood lamp may include:
A variety phosphors with different peak emission
Magnifying lens
White light
Black drape to exclude light
Describe a Wood lamp skin examination
Examination using Wood lamp involves the following steps.
Ideally, skin to be examined should not have been recently washed or had any makeup, deodorant or moisturising
cream
applied, as these can fluorescence causing a false positive result
Gentle facial skin cleansing may be required
The Wood lamp is turned on to warm up for about a minute
Room lights are turned off, and window shades are drawn, or black drape used to darken the surroundings completely
After waiting to adapt to the dark, the skin is examined with Wood lamp for a few seconds. The lamp is held about 10-30 cm away from the skin. The examination is painless and safe.
A Wood lamp is used to identify the extent of
pigmented
or depigmented patches and to detect fluorescence. Normal healthy skin is slightly blue but shows white spots where there is thickened skin, yellow where it is oily, and purple spots where it is dehydrated. Clothing lint often shines bright white.
A positive result is reported if a
pigmentary
disorder is more noticeable when examined using the Wood lamp or if fluorescence is noted.
What is fluorescence?
Fluorescence is a coloured glow seen when certain substances such as
collagen
and
porphyrins
absorb black light and emit it again at a longer wavelength in the visible spectrum. Items on the skin surface such as fabric,
topical
medications and soap residue can also fluoresce.
What conditions are diagnosed using a Wood lamp?
A Wood lamp for skin examination may reveal:
Increase in
pigmentation
(eg,
melasma
,
postinflammatory
pigmentation
) to determine whether the pigmentation is
epidermal
(pigmentation enhanced by Wood lamp examination) or
dermal
(pigmentation unchanged by Wood lamp examination). Pigmented
lesions
have a clear border under Wood light because the light is absorbed by increased
melanin
Loss of pigmentation (eg,
vitiligo
, ash-leaf
macules
in
tuberous
sclerosis
, and
hypomelanosis
of Ito
) to identify affected areas in light-skinned people.
Hypopigmented
skin has sharper borders under black light and fluoresces bright blue-white (or sometimes, yellowish green) due to accumulated biopterins. In contrast, areas of reduced blood flow are unchanged
Pityriasis
versicolor
—a slightly
scaly
persistent
rash
on
anterior
chest and back caused by
Malassezia
yeasts. When active, the
scale
emits a yellowish or orange glow
Malassezia folliculitis
—hair
follicles
fluoresce bluish-white
Tinea capitis
—areas of scale and baldness due to
fungal
infection
. Microsporum species fluoresce blue-green (
M canis, M audouinii, M ferrugineum, M distortum
);
Trichophyton schoenleinii
fluoresces dull blue. Fungal infection due to other
organisms
does not fluoresce
Head lice
and
scabies
Erythrasma
—corynebacteria
bacteria
cause a pigmented rash in skin folds that fluoresces a coral-pink colour
Pseudomonas
in
spa pool folliculitis
and
wound infection
fluoresces green
Acne
fluoresces orange-red due to
cutibacteria
in hair follicles
Porphyria
causes red-pink fluorescence of the skin (
porphyria cutanea tarda
), or teeth (
erythropoetic porphyria
)
Porphyrins used as the photosensitiser in
photodynamic
therapy
Drugs on the skin surface—
tetracyclines
and mepacrine fluoresce after oral
ingestion
The evenness of application of a
salicylic acid
-containing chemical peel (this fluoresces green).
Other uses for Wood lamp
Apart from Wood lamp skin examination, the Wood lamp has other uses.
Biochemistry laboratory may look for signs of porphyria in red blood cells (
erythropoietic protoporphyria
), urine and stool (
porphyria cutanea tarda
)
Molecular
biology laboratory may use a Wood lamp to detect compounds with a fluorescent tag
Aestheticians check for signs of
ageing skin
and other imperfections
Ophthalmologists look for scratches and foreign bodies in the
cornea
of the eye
Veterinary surgeons
use the Wood lamp when examining pets for
bacterial
, fungal or parasitic infection
Law enforcement officers examine crime scenes and clothing for semen and urine
Pet
or rodent urine/faeces is easily detected using a Wood lamp
Metal fatigue can be evaluated using a fluorescent fluid and Wood lamp examination
Nightclubs use a Wood lamp to check fluorescent re-entry stamps
Immigration officers check that passports are genuine
Banks check for counterfeit money
Mineralogy and gemology
Displaying fluorescent paint used in art and sculpture
Does the Wood lamp cause any harm?
The black light emitted by a Wood lamp is harmless. The lamp does not emit short-wavelength ultraviolet B radiation (290–320 nm), so it does not cause
sunburn
or otherwise damage healthy skin.