Many pet owners have heard of the black light lamp and have even had their own cats in the hospital with the black light lamp. It is said to be a miracle tool for detecting ringworm in cats, so what is its magic?

Let’s dive right in now, and you can click on the question that interest you, 

1 The origin of black light lamp

black light lamps, also known as ultraviolet lamps or Wood’s lamps, are lamps that emit long-wave ultraviolet light (UV-A) and a small amount of visible light, also called UV-A lamps, black lamps have dark violet filter material on the electric bulb or in separate glass filters that are used to filter visible light while allowing UV light to pass through, but sometimes the visible light is not completely filtered and is activated when emitting a visible violet light. These black light bulbs with filtering material are marked in the industry with the letters “BLB” (black light bulb).

Black Light Lamp

Wood’s lamp can emit ultraviolet light of 320 nm~400 nm wavelength, which is a long wave of ultraviolet light and is not damaging to the skin or eyes. In clinical practice, Wood’s lamp can be used not only for detecting ringworm but also for detecting vitiligo as well as detecting the presence of urine and feces.

2 The principle of black light lamp

Why does black light lamp detect ringworm in cats? The principle is simple. Because different fungi fluoresce in different colors under the Wood’s lamp (ultraviolet light), and with the help of the different fluorescence, you can determine the type of fungus. Here are the colors of some common fungi under Wood’s lamp.

  • Microsporum canis – apple green
  • Microsporum rusticum-blue-green
  • Microsporum gypsum-dark yellow
  • Stachybotrys hirsutus-pale blue
  • Coccidioides-yellow-green
  • Vitiligo – blue-white to bright white fluorescence
  • Microsporum Canis – green fluorescence
  • Microsporidium – light green fluorescence
  • Stachybotrys yellow – dark green fluorescence
  • Aspergillus flavus – blue to green fluorescence

Black Light Lamp

As can be seen, in addition to fungal infections, there are other types of diseases or factors that can cause the black light lamp to fluoresce, such as bacterial infectious diseases and parasites such as mange mites, and also some pharmaceutical ingredients. Some detergent ingredients may also cause fluorescence under the black light lamp, similar to the reaction to ringworm.

3 Black light lamp and catarrh

The black light lamp can be an important tool in determining ringworm in cats, but the Wood’s lamp is not a 100% conclusive way to diagnose it.

More than 98% of ringworm in cats is caused by Microsporum canis and Microsporum gypsum. Microsporum canis and Microsporum spp. will fluoresce green when illuminated by a Wood’s lamp, so does a green fluorescence on a cat mean it must have cat moss?

Not necessarily.

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As you can see from the table above, in addition to Microsporum, Pseudomonas aeruginosa, Sarcoptes scabiei, Tinea albicans, and Tinea flavus are capable of causing a green fluorescent reaction. It can only be said that ringworm infection can in most cases have a fluorescent reaction under Wood’s lamp, but a fluorescent reaction is not necessarily ringworm. A careful skin examination is also usually performed in the clinical diagnosis and treatment of ringworm that matches the symptoms of ringworm:

  • Most commonly occurring on the face, trunk, limbs, and tail of cats.
  • Loss of hair from the affected area, exposing round patches covered with skin flakes.
  • Large areas of skin shedding and the formation of red patches or scabs.
  • The cat feels intense itching and scratches the affected area causing redness, swelling, and erosion, which can be severe enough to turn into pus.

In addition, the doctor will use a variety of methods such as microscopy, fungal culture, PCR, histopathology, and immunological testing to confirm the diagnosis. If you go to a hospital to treat your cat for ringworm and the doctor only uses a Wood’s lamp to confirm the diagnosis, it is better to go to a different hospital~

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As a final note, cats infected with Microsporum canis may not show 100% of the symptoms of ringworm, but some may just shed a little more hair, have occasional itchy skin, or even have no symptoms at all. However, if the owner has a weak resistance, he or she may be infected by your cat, as ringworm is a zoonotic disease. Whether or not ringworm manifests itself depends on the body type and immunity of the individual, so it is important to pay attention to improving nutrition and resistance.