Table of ContentsView All

View All

Table of Contents

How a Wood’s Lamp Works

What to Expect

Interpreting Results

Frequently Asked Questions

A Wood’s lamp is a device that emits purple or violet UV rays. When placed over your skin, it can help your healthcare provider diagnose conditions that affect the skin and hair, including fungal and bacterial infections, lice, and pigment irregularities.

Normal, healthy skin will not glow under the lamp. Some kinds of bacteria, fungi, and other skin conditions will.

This article explains how a Wood’s lamp works to detect skin and hair conditions. It also covers the conditions it can help diagnose and what you can expect during the exam.

Also Known AsThe Wood’s lamp was named for the physicist who invented it. The exam is also sometimes called:Black light testUltraviolet light test

Also Known As

The Wood’s lamp was named for the physicist who invented it. The exam is also sometimes called:Black light testUltraviolet light test

The Wood’s lamp was named for the physicist who invented it. The exam is also sometimes called:

A healthcare provider turns on a Wood’s lamp and holds it over areas of your skin or hair to look for signs of an infection or other condition. A magnifying glass over the light provides a close-up look.

Inside Creative House/ Getty Images

Cropped shot of dermatologist using the Wood Lamp for diagnosis of skin condition

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

Here are some of the conditions that can be diagnosed using a Wood’s lamp and how each one appears under the light:

Vitiligo on Darker Skin

A Wood’s lamp exam is non-invasive, painless, quick, and safe. Here’s what to know about how this exam is done.

Who Does the Test

Estheticiansmay also use these lamps to check for signs of aging like uneven skin tone, wrinkles, and age spots before beginning a cosmetic treatment. While these professionals specialize in providing skincare treatments, they are not medical professionals and cannot formally diagnose you with any condition.

How to Prepare

Your skin should be clean and dry before the exam. Do not apply any perfumes, makeup, lotions, or other skincare products.

These may show up under the light and affect the results, either indicating there may be a problem when there is not or making something that truly is a concern less noticeable.

During the Test

A Wood’s lamp exam must be performed in a completely dark room.

First, your healthcare provider will turn on the lamp and let it warm up for about a minute. Then they will hold the lamp about 4 to 5 inches away from your skin and hair and examine each area for a couple of seconds.

You will be asked to cover your eyes or wear special goggles during a Wood’s lamp exam to avoid damage to your corneas, the dome-like structures that help your eyes focus.

Although any medical professional can do a Wood’s lamp exam, it is highly recommended that a dermatologist interprets the results.

After reviewing your symptoms and conducting a Wood’s lamp exam, your doctor may have enough information to diagnose your skin condition and move ahead with treatment.

This chart summarizes the possibilities:

ConditionColor Under Wood’s LampBacterial infectionsBright greenErythrasmaCoral/pinkHead liceWhite or grayPigment irregularitiesBright blue/whitePityrosporum folliculitisYellow/greenPorphyriaReddish pinkRingwormBlue/greenVitiligoBright blue/white or yellow/greenIt’s also possible they may need to perform other types of tests to get an accurate diagnosis.SummaryA Wood’s lamp emits long UV rays that can help identify various skin conditions. When the light shines on the skin and hair, fungal and bacterial infections, pigmentation abnormalities, lice, and other conditions will illuminate. The colors that they “light up” can guide a diagnosis.A Wood’s lamp exam is brief, painless, and safe. If your doctor diagnoses you with a skin condition, the next step will to receive the appropriate treatment.How to Tell If You Need a DermatologistFrequently Asked QuestionsThere are no significant risks associated with a Wood’s lamp examination. The type of light used does not irritate or burn the skin. You will be asked to cover your eyes during the exam to avoid any damage to the cornea.Healthy skin doesn’t glow under a Wood’s lamp and appears blue.The light these devices emit is the same, though they are constructed differently. A Wood’s lamp exam is sometimes called a black light test.

It’s also possible they may need to perform other types of tests to get an accurate diagnosis.

Summary

A Wood’s lamp emits long UV rays that can help identify various skin conditions. When the light shines on the skin and hair, fungal and bacterial infections, pigmentation abnormalities, lice, and other conditions will illuminate. The colors that they “light up” can guide a diagnosis.

A Wood’s lamp exam is brief, painless, and safe. If your doctor diagnoses you with a skin condition, the next step will to receive the appropriate treatment.

How to Tell If You Need a Dermatologist

Frequently Asked QuestionsThere are no significant risks associated with a Wood’s lamp examination. The type of light used does not irritate or burn the skin. You will be asked to cover your eyes during the exam to avoid any damage to the cornea.Healthy skin doesn’t glow under a Wood’s lamp and appears blue.The light these devices emit is the same, though they are constructed differently. A Wood’s lamp exam is sometimes called a black light test.

There are no significant risks associated with a Wood’s lamp examination. The type of light used does not irritate or burn the skin. You will be asked to cover your eyes during the exam to avoid any damage to the cornea.

Healthy skin doesn’t glow under a Wood’s lamp and appears blue.

The light these devices emit is the same, though they are constructed differently. A Wood’s lamp exam is sometimes called a black light test.

5 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.DermNet NZ.Wood lamp skin examination.Sharma S, Sharma A.Robert Williams Wood: pioneer of invisible light.Photodermatol Photoimmunol Photomed. 2016;32(2):60-65. doi:10.1111/phpp.12235University of Michigan Health.Pseudomonas infection.Bonilla C, Ness AR, Wills AK, Lawlor DA, Lewis SJ, Davey Smith G.Skin pigmentation, sun exposure and vitamin D levels in children of the Avon Longitudinal Study of Parents and Children.BMC Public Health. 2014;14(1):597.Mount Sinai.Wood’s lamp examination.Additional ReadingBonilla C, Ness AR, Wills AK, Lawlor DA, Lewis SJ, Davey Smith G.Skin pigmentation, sun exposure and vitamin D levels in children of the Avon longitudinal study of parents and children.BMC Public Health. 2014;14(1):597.Rastegar Lari AR, Alaghehbandan R, Akhlaghi L.Burn wound infections and antimicrobial resistance in tehran, iran: an increasing problem.Ann Burns Fire Disasters.2005;18(2):68-73.

5 Sources

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.DermNet NZ.Wood lamp skin examination.Sharma S, Sharma A.Robert Williams Wood: pioneer of invisible light.Photodermatol Photoimmunol Photomed. 2016;32(2):60-65. doi:10.1111/phpp.12235University of Michigan Health.Pseudomonas infection.Bonilla C, Ness AR, Wills AK, Lawlor DA, Lewis SJ, Davey Smith G.Skin pigmentation, sun exposure and vitamin D levels in children of the Avon Longitudinal Study of Parents and Children.BMC Public Health. 2014;14(1):597.Mount Sinai.Wood’s lamp examination.Additional ReadingBonilla C, Ness AR, Wills AK, Lawlor DA, Lewis SJ, Davey Smith G.Skin pigmentation, sun exposure and vitamin D levels in children of the Avon longitudinal study of parents and children.BMC Public Health. 2014;14(1):597.Rastegar Lari AR, Alaghehbandan R, Akhlaghi L.Burn wound infections and antimicrobial resistance in tehran, iran: an increasing problem.Ann Burns Fire Disasters.2005;18(2):68-73.

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

DermNet NZ.Wood lamp skin examination.Sharma S, Sharma A.Robert Williams Wood: pioneer of invisible light.Photodermatol Photoimmunol Photomed. 2016;32(2):60-65. doi:10.1111/phpp.12235University of Michigan Health.Pseudomonas infection.Bonilla C, Ness AR, Wills AK, Lawlor DA, Lewis SJ, Davey Smith G.Skin pigmentation, sun exposure and vitamin D levels in children of the Avon Longitudinal Study of Parents and Children.BMC Public Health. 2014;14(1):597.Mount Sinai.Wood’s lamp examination.

DermNet NZ.Wood lamp skin examination.

Sharma S, Sharma A.Robert Williams Wood: pioneer of invisible light.Photodermatol Photoimmunol Photomed. 2016;32(2):60-65. doi:10.1111/phpp.12235

University of Michigan Health.Pseudomonas infection.

Bonilla C, Ness AR, Wills AK, Lawlor DA, Lewis SJ, Davey Smith G.Skin pigmentation, sun exposure and vitamin D levels in children of the Avon Longitudinal Study of Parents and Children.BMC Public Health. 2014;14(1):597.

Mount Sinai.Wood’s lamp examination.

Bonilla C, Ness AR, Wills AK, Lawlor DA, Lewis SJ, Davey Smith G.Skin pigmentation, sun exposure and vitamin D levels in children of the Avon longitudinal study of parents and children.BMC Public Health. 2014;14(1):597.Rastegar Lari AR, Alaghehbandan R, Akhlaghi L.Burn wound infections and antimicrobial resistance in tehran, iran: an increasing problem.Ann Burns Fire Disasters.2005;18(2):68-73.

Bonilla C, Ness AR, Wills AK, Lawlor DA, Lewis SJ, Davey Smith G.Skin pigmentation, sun exposure and vitamin D levels in children of the Avon longitudinal study of parents and children.BMC Public Health. 2014;14(1):597.

Rastegar Lari AR, Alaghehbandan R, Akhlaghi L.Burn wound infections and antimicrobial resistance in tehran, iran: an increasing problem.Ann Burns Fire Disasters.2005;18(2):68-73.

Meet Our Medical Expert Board

Share Feedback

Was this page helpful?Thanks for your feedback!What is your feedback?OtherHelpfulReport an ErrorSubmit

Was this page helpful?

Thanks for your feedback!

What is your feedback?OtherHelpfulReport an ErrorSubmit

What is your feedback?

By clicking “Accept All Cookies”, you agree to the storing of cookies on your device to enhance site navigation, analyze site usage, and assist in our marketing efforts.Cookies SettingsAccept All Cookies

By clicking “Accept All Cookies”, you agree to the storing of cookies on your device to enhance site navigation, analyze site usage, and assist in our marketing efforts.

Cookies SettingsAccept All Cookies