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Erythrasma is a skin infection caused by a gram positive anaerobic bacillus known as Corynebacterium Minutissimum and Erythrasma occurs in intertriginous area - where two skin areas touch or rub together. Overlapping skin helps to propagate the bacteria. The result is scaly skin fold patches slowly enlarging and gradually changing the skin color to pink or brown dry skin. Erythrasma looks like a patch of red to pink scaly skin. The border of the infection is well defined, that is, there is a sharp patch between the patch and the surrounding normal skin. In course of time the pink skin takes a brown or tan shade. Erythrasma is more common in warm climates. It is more common in dark skinned individuals.

Erythrasma risk factors

There are contributory factors that increase the chances of Erythrasma.

  • Warm, humid climate
  • Poor hygiene
  • Increased/excessive sweating
  • Diabetes
  • Advanced age
  • Poor immune function

Erythrasma Variants

Two distinct variants of Erythrasma are generalized Erythrasma and inter digital Erythrasma. Of the two, inter digital is most common. The infection happens in the feet, the inter spaces of the toes, particularly the fourth or fifth toe of the feet. The generalized variant is seen in diabetics (Type 2 diabetes). Herein, the skin lesions may extend beyond the intertriginous areas.

Diagnosing Erythrasma

Patches may appear in the groin, armpits, under the breasts and skin folds. It may itch slightly or the person may experience burning sensation. There is a possibility of the infection spreading. It occurs most commonly in the foot, where it causes scaling, cracking and breakdown of the skin between the 4th and 5th toes. In middle aged women, the skin folds under the breasts, on the abdomen and the area between the vaginal opening and the anus are prone to this infection. It could also spread to the torso and the anal area in some.

  • Skin appears pink or brown and dry.
  • Reddish-brown slightly scaly patch with sharp borders on the affected skin area.
  • Occurs in groin, armpit as well as other skin folds.
  • Mild itching or burning especially in the groin area.
  • Mild headaches, fatigue, swelling, weight gain.
  • Pain in abdomen, chest, back, joint, urinary tract.

If diabetic, the infection can involve the arms, trunk and the leg. Without ignoring it as a fungal infection and resorting to self care measures, seek medical help.

Erythrasma Diagnosis

To confirm that the rashes aren't due to any fungal infection, a wood's lamp examination - (under Ultra Violet light) is the most preferred choice. Fix up an appointment with the dermatologist for the examination. The procedure is performed in a dark room. For few seconds, ultraviolet light is directed on the affected area. In Erythrasma, a bright coral-red fluorescence is seen. Any change in color confirms the diagnosis.

If the results are negative, the doctor may recommend culture test of the scrapings from the lesion, or microscopic examination of skin scrapings. Few areas may be scraped to gather specimens to be sent to the lab for definite diagnosis.

Erythrasma Treatment

After confirming diagnosis, Erythrasma treatment is related to the infection being localized, extensive or frequent recurrences. Photo dynamic therapy using a red light is used in some cases to clear Erythrasma and to improve the rash in the remaining patients. Complete recovery is expected in each of the following procedures.

Localized Erythrasma: Topical application of erythromycin or clindamycin 1% two to three times daily for 14 days or washing twice daily with an antibacterial soap for up to three weeks. Solution of aluminum chloride inhibits moisture and sweating as Erythrasma occurs in moist skin, this could be used. Whitfield's ointment which is a mixture of benzoic acid and salicylic acid is also prescribed for Erythrasma.

Extensive involvement: Oral erythromycin or clarithromycin

Frequent recurrences: Prophylactic therapy combined with the use of antibacterial soap during bathing.

Prevention tips

There are simple ways to prevent Erythrasma.

Ensure that skin is dry after shower and before dressing to reduce possibility of bacteria to grow on the damp areas of the skin.

Use antibacterial soap instead of regular soap to prevent recurrence.

Maintaining ideal weight and not being obese and keeping sugar under control also helps in prevention of the infection.

Wood's Lamp Examination

A wood's lamp examination helps the doctor confirm a fungal infection or bacterial infection. The doctor is able to determine the cause of any light or dark colored spot on the skin using this examination. This is a test using Ultraviolet or UV light to look more closely at the skin.

In case of fair skinned individuals, Wood's lamp can detect Vitiligo or any other depigmentation even when it is not visible to the eye under normal conditions. In case of detection, Vitiligo can be treated at an early stage even before it is visible to the normal eye, thereby minimizing treatment and preventing further expansion of the disorder.

What is Wood's lamp?

Also known as Black Light Test, or Ultraviolet Light Test, this is based on the use of ultraviolet light which is shined on the area being examined, when performed in a dark room. It emits ultraviolet light in the 365 nanometer range and when the light is shined directly on the area in darkness, the dermatologist looks for any change in color or fluorescence. While normal skin does not fluoresce under the light of the Wood's lamp, affected skin 'glows' in dark. if any fungal or bacterial infection or pigment is present, the Wood's lamp can strengthen or lessen the suspicion of a particular diagnosis based on the color of florescence of the affected skin being illuminated. Even subtle color changes can be detected very well using Wood's lamp.


You will be seated in a dark room usually in the dermatologist's office. The doctor turns on the Wood's lamp and holds it approximately 5 inches from the skin to look for color changes. It will reveal skin color changes not visible to the mere eye examination. The patient is advised not to look directly into the light when being examined. This portion of the examination usually lasts for less than a minute and the patient feels no discomfort from the examination.

Pre and post procedure

Before the Wood's lamp examination do not wash the area or apply any cream to the skin to avoid inaccurate results. Following the procedure, the dermatologist may decide to treat the skin condition based on the results of the Wood's lamp examination. Additional tests are sometimes done to arrive at the correct diagnosis. No aftercare is recommended specific to the examination and depending on the result of the examination the physician may recommend treatment of a skin disorder.

Why is Wood's lamp examination done?

Certain skin problems including bacterial and fungal infections, Porphyria, skin coloring changes in Vitiligo, head lice and nits, Erythrasma and other pigmentary disorders can be performed using this test.

The test also reveals different colors according to the type of the skin disease which includes:

  • Golden Yellow: Tinea Versicolor
  • Pale Green: Trichophyton Schoenleini
  • Bright Yellow green: Microsporum Audouini or M. Canis
  • Aquagreen To Blue: Pseudomonas Aeruginosa
  • Pink To Pink orange: Porphyria Cutanea Tarda
  • Ash-Leaf-Shaped Spot: Tuberous Sclerosis
  • Blue white: Leprosy
  • Pale White: Hypopigmentation
  • Purple brown: Hyperpigmentation
  • Bright White, Or Blue white: Depigmentation, Vitiligo
  • Bright White: Albinism If it is a normal result, the skin will not shine under the ultraviolet light.


Exposure to Ultra violet Light for prolonged duration can result in skin damage and cancer of the skin. But this test hardly lasts for a minute and the intensity of the light is minimal. Patients should avoid looking directly into the UV light and since the time for the procedure is very minimal - less than a minute - the procedure is well tolerated as there is no associated pain and no side effects as a result. Beware that the presence of other materials like certain kind of makeup, deodorants, perfume, body lotion or soap can also fluoresce leading to difficulty in arriving at a conclusive diagnosis. Equally if the room is not dark enough, it may present difficulty for proper examination. Not all bacteria or fungi show up under the UV light.

Tags: #Erythrasma #Wood's Lamp Examination
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Collection of Pages - Last revised Date: June 25, 2024