Wood’s Lamp Examination Test

Wood’s Lamp Examination Test

Skin Care
Laboratory Procedures
Contributed byMaulik P. Purohit MD MPHMay 26, 2019

What are other Names for this Test? (Equivalent Terms)

  • Wood’s Lamp UV Examination Test
  • Black Light Examination Test
  • Ultraviolet Light Examination Test

What is the Wood’s Lamp Examination Test? (Background Information)

  • The Wood’s Lamp Examination Test uses ultraviolet (UV) light to detect skin abnormalities.
  • UV light is a form of high-energy light. It is often used to detect certain substances by making them glow.
  • Natural fluids, such as those from plants and animals, glow when exposed to UV light because of the presence of proteins that contain UV-absorbing amino acids. Specifically, certain amino acids – tyrosine and tryptophan – absorb UV light.
  • After they absorb UV light, the tyrosine and tryptophan in proteins emit lower-energy light that creates a distinct glow.
  • Other non-protein natural compounds also glow when exposed to UV light. An example is a class of compounds called porphyrins, which are associated with the body’s production of hemoglobin.
  • The accumulation of porphyrins may indicate that the assembly-line production of hemoglobin has gone wrong. This is called porphyria. It mainly occurs when enzymes malfunction, either because of genetic disorders or toxicity caused by heavy metals.
  • Bacteria and fungi also produce compounds that glow when exposed to UV light. Thus, bacterial and fungal infections of the skin may be detected by shining them with UV light.
  • The Wood’s Lamp Examination Test uses UV light to detect infections, porphyrias, and skin abnormalities. Various body fluids, such as urine, saliva, pleural effusion fluid, and peritoneal effusion fluid, may be tested depending upon the clinical situation, and several skin condition may be examined by the test

What are the Clinical Indications for performing the Wood’s Lamp Examination Test?

Clinical indications for performing the Wood’s Lamp Examination Test include:

  • Exposure to heavy metals
  • Nausea and vomiting
  • Abdominal pain
  • Hallucinations
  • Disruptions to cognition and thinking
  • Tingling in extremities
  • Appearance of new skin pigmentation
  • Discolored feces
  • Rash
  • Itching
  • Redness
  • Pain

How is the Specimen Collected for the Wood’s Lamp Examination Test?

  • Sample required:
  • Any body fluid such as urine, saliva, pleural fluid, and peritoneal fluid
  • No specific sample is required in case of a skin condition for this test, apart from the presence of the affected individual
  • Process:
    • Process of examining the skin lesion
    • Darkening the room
    • Shining a Wood’s lamp 4 to 5 inches from the skin
    • Process of examining the body fluid: The fluid to be examined is collected in a test tube and examined by shining a Wood’s lamp on the fluid
  • Preparation required: No special preparation is needed for the skin examination
  • Avoid beverages such as club soda which contains quinine, which can lead to a false positive test result, prior to the body fluid exam

What is the Significance of the Wood’s Lamp Examination Test Result?

A positive value for the Wood’s Lamp Examination Test is indicated by a glow when exposed to UV light. This may mean:

  • Bacterial infection
  • Fungal infection
  • Vitiligo
  • Porphyria

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results in the context of the overall clinical scenario.

Additional and Relevant Useful Information:

  • Certain factors interfere with the results of the Wood’s Lamp Examination Test. These include the use of cosmetic products, soaps, and deodorants.
  • Examining body fluids after consumption of certain beverages such as club soda may give a false positive result
  • Club soda glows under UV light because of the presence of quinine. Quinine is a naturally occurring product extracted from the cinchona tree. It may also be synthesized artificially.

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

Please visit our Laboratory Procedures Center for more physician-approved health information:


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Maulik P. Purohit MD MPH picture
Approved by

Maulik P. Purohit MD MPH

Assistant Medical Director, Medical Editorial Board, DoveMed Team


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