What is a Wood Lamp Inspection?

A Wood lamp is a device that emits violet or violet ultraviolet light. When placed on your skin, it can help your healthcare provider diagnose conditions that affect your skin and hair, including fungal and bacterial infections, lice, and pigment abnormalities.

Normal, healthy skin does not glow under lights. Certain kinds of bacteria, fungi, and other skin conditions can.

This article explains how Wood lights detect skin and hair conditions. It also covers the situations it can help diagnose and what you can expect during the exam.

also known as

Wood’s lamp is named after the physicist who invented it. Exams are also sometimes called:

  • black light test
  • UV test

How wooden lamps work

A healthcare provider turns on a Wood lamp and places it on your skin or hair area to look for signs of infection or other conditions. A magnifying glass above the light provides a close-up view.

Healthy skin looks just blue under Wood’s light. But bacteria, fungi, and abnormal areas of the skin have what’s called fluorescence. This means they absorb the wavelengths of light emitted by the lamp and essentially “convert” it to different wavelengths. This makes the affected area glow.

The color of the glow varies according to the type of skin condition.

Conditions diagnosed with wooden lamps

Here are some of the conditions that can be diagnosed using a Wood lamp, and how each condition behaves under the light:

  • Bacterial infections: Bacterial infections, especially Pseudomonas infections, are bright green under Wood’s lamp. These infections tend to affect people who are hospitalized or burned. This type of infection can lead to a dangerous complication called sepsis.
  • Erythrasma: Skin infections caused by bacteria called bacteria Corynebacterium parvum. It shows up as a coral pink under the Wood light.
  • Head Lice: On Wood’s lamp examination, head lice larvae are white, while empty louse egg boxes are grey.
  • Abnormal pigmentation: Wood’s light can detect an abnormal amount of pigmentation. The lack of pigmentation gives a bright bluish-white under the Wood light. Hyperpigmentation looks darker with sharper borders.
  • Pityrosporum folliculitis (Fungal acne): This is a yeast infection that affects the hair follicles. It can be found on your chest and upper back. It is difficult to detect because it resembles acne. It looks yellow-green under Wood lights.
  • Porphyria: A group of rare diseases that affect your skin and nervous system. People with porphyria are particularly sensitive to the sun and can burn their skin. Under Wood’s lamp, porphyria are usually reddish-pink.
  • Ringworm: A fungal infection that usually causes itchy, round, red patches. Despite the name, the worm does not cause this infection. Ringworm is blue-green under Wood’s lamp.
  • Vitiligo: A skin disorder that removes skin color from patches by killing melanin-producing cells. Vitiligo will have clear borders under Wood’s lamp and will appear bright blue-white or yellow-green.

How to Diagnose Vitiligo

what to expect

Wood’s lamp examinations are non-invasive, painless, quick and safe. Below is information on how to complete this exam.

who does the test

Wood’s lamp tests can be performed by any type of medical professional, but these tests are usually performed in their office by a dermatologist (a doctor who specializes in skin diseases).

beautician These lights can also be used to check for signs of aging, such as uneven skin tone, wrinkles, and age spots, before starting a cosmetic treatment. While these professionals specialize in skin care treatments, they are not medical professionals and cannot formally diagnose any of your conditions.

How to prepare

Your skin should be clean and dry before the test. Do not use any perfume, makeup, lotion or other skin care products.

These can show up in the lights and affect the results, either indicating a possible problem or not really worrying.

During the test

Wood lamp inspections must be performed in a completely dark room.

First, your healthcare provider will turn on the lights and let it warm up for about a minute. They will then place the light about 4 to 5 inches from your skin and hair and examine each area for a few seconds.

During a Wood’s lamp exam, you’ll be asked to cover your eyes or wear special goggles to avoid damaging your cornea, the dome-shaped structure that helps your eye focus.

Interpret the results

Although any medical professional can perform a Wood’s lamp test, a dermatologist is strongly advised to interpret the results.

After reviewing your symptoms and having a Wood’s lamp test, your doctor may have enough information to diagnose your skin condition and continue treatment.

This chart summarizes the various possibilities:

State of health color under wooden lights
Bacterial infections bright green
Erythrasma coral/pink
head lice white or grey
Irregular Pigment bright blue/white
Pityrosporum folliculitis yellow-green
Porphyria red pink
Ringworm blue-green
vitiligo Bright blue/white or yellow/green

They may also need other types of tests to get an accurate diagnosis.

generalize

Wood’s lamps emit long UV rays that help identify various skin conditions. Fungal and bacterial infections, dyspigmentation, lice, and other conditions shine when light hits the skin and hair. The color they “light up” can guide diagnosis.

Wood lamp exams are short, painless, and safe. If your doctor has diagnosed you with a skin condition, the next step is to receive appropriate treatment.

How to tell if you need a dermatologist

Frequently Asked Questions

  • Are there any risks to using a Wood lamp?

    There are no major risks to a Wood lamp inspection. The type of light used will not irritate or burn the skin. You will be asked to cover your eyes during the exam to avoid any damage to the cornea.

  • How should normal skin look under Wood’s lamp?

    Healthy skin doesn’t glow under the Wood’s lamp, it’s blue.

  • What is the difference between a wood light and a black light?

    The light emitted by these devices is the same, although they are constructed differently. The Wood lamp inspection is sometimes called the black light test.

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5 sources

VigorTip Health uses only high-quality resources, including peer-reviewed research, to support the facts in our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable and trustworthy.

  1. New Zealand Skin Network. Wood lamp skin examination.

  2. Sharma S, Sharma A. Robert Williams Wood: Pioneers of Invisible Light. Photodermatol Photoimmunol Photomed2016;32(2):60-65. doi:10.1111/phpp.12235

  3. University of Michigan Health. Pseudomonas infection.

  4. Bonilla C, Ness AR, Wills AK, Lawlor DA, Lewis SJ, Davey Smith G. Avon Parent and Child Longitudinal Study of Skin Pigmentation, Sun Exposure, and Vitamin D Levels in Children. BMC Public Health2014;14(1):597.

  5. Mount Sinai. Wood lamp inspection.

Additional reading

  • Bonilla C, Ness AR, Wills AK, Lawlor DA, Lewis SJ, Davey Smith G. Children’s skin pigmentation, sun exposure, and vitamin D levels in the Avon Longitudinal Study of Parents and Children. BMC Public Health2014;14(1):597.

  • Rastegar Lari AR, Alaghehbandan R, Akhlaghi L. Burn infection and antimicrobial resistance in Tehran, Iran: a growing problem. Ann burns fire. 2005;18(2):68-73.

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