What Is Erythrasma?

This bacterial skin infection is linked to humidity and diabetes

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Erythrasma

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Erythrasma is a superficial infection caused by a bacteria known as Corynebacterium minutissimum, which naturally resides on the body. It is characterized by the development of a discolored patch, primarily in folds of skin. There are two types: Interdigital erythrasma primarily develops between the toes, while generalized erythrasma is more widespread and commonly seen in people with type 2 diabetes. The rash itself is not considered serious but may serve as an early warning sign of a more serious condition.

Symptoms

Erythrasma starts as a pinkish patch of skin that quickly turns brown and scaly as the outer layers start to shed. The infection mainly occurs in so-called intertriginous areas where two skin areas touch or rub together. These include the armpits, groin, navel, under the breasts, and between the toes. The patches may cause mild itching and have regular or irregular borders.

Most people will experience interdigital erythrasma, primarily in the webbing of the third, fourth, and fifth toes. Generalized erythrasma is more widespread and will often move beyond intertriginous areas to the trunk and torso.

An erythrasma infection is typically self-limiting and will often resolve on its own without treatment. While complications are rare, erythrasma can sometimes co-occur with contact dermatitis, a fungal infection, or an unrelated bacterial infection. In such instances, a C. minutissimum infection may spread to deeper layers of skin and lead to the development of an abscess or potentially serious skin infection known as cellulitis.

Causes

C. minutissimum is considered a relatively harmless bacterium that the immune system is usually able to control. It will only cause infection if the right conditions provide the bacteria the opportunity to thrive. It may be because a skin fold offers just the right environment for bacterial colonization or the immune system is suppressed and less able to control an infection.

Generally speaking, you are more likely to develop erythrasma if you:

  • Live in a humid tropical or subtropical climate
  • Sweat excessively (known as hyperhidrosis)
  • Have poor hygiene
  • Are older
  • Have HIV or other forms of immune suppression
  • Take immune suppressive drugs to treat an autoimmune disorder or prevent organ rejection
  • Are obese
  • Have diabetes

Obesity is known to reduce the body's response to infection while providing more skin folds to establish an infection. Similarly, widespread infections are associated with poorly controlled diabetes.

All told, around 4 percent of the world's population will experience erythrasma at least once in their life, particularly those living in tropical or subtropical regions. For reasons not entirely clear, African Americans are more prone to erythrasma than other racial or ethnic groups in the United States.

Diagnosis

Erythrasma can often be diagnosed by appearance alone. The characteristic brown patch with fine scaling helps distinguish it from fungal infections like tinea cruris (jock itch), which are more reddish and have thicker scaling along the edges.

If in doubt, the doctor may use a specialized ultraviolet light, known as a Wood's lamp, which will cause the bacteria to fluoresce in a coral-pink color. A Wood's lamp can only help diagnose certain infections but may differentiate erythrasma from other skin conditions. Among them:

  • Microsporum fungal infections, such as ringworm, will turn a dull blue.
  • Pseudomonas bacterial infections, such as hot tub folliculitis, will turn green.
  • Malassezia fungal infections, also associated with folliculitis, will turn a bluish white.
  • Intertrigo rash, caused by skin-to-skin friction, will also turn green.
  • Inverse psoriasis, a type of psoriasis found in skin folds, will often turn red.
  • Tinea versicolor, a fungal infection, will turn a copper-orange.

If the condition is serious or recurrent, bacterial and fungal cultures may be performed to see if there are any co-existing infections.

Recurrent or widespread erythrasma may warrant a random blood glucose test or fasting blood glucose test as a first step toward diagnosing type 2 diabetes.

Treatment

The primary treatment of erythrasma would involve the use of an antibacterial soap to resolve a mild infection.

If the infection is more widespread, a topical antibiotic or microbicide may be prescribed. The most effective include 2% clindamycin, Fucidin ointment (sodium fusidate), and Whitfield's ointment (benzoic acid plus salicylic acid). Treatment is typically prescribed for one to two weeks with twice-daily application. Side effects may include rash, redness, drying, itching, and nausea.

Serious infection may require oral antibiotics, including clarithromycin, erythromycin, tetracycline, and chloramphenicol. Treatment may require as little as a single dose (for clarithromycin) or up to a five-day course (for erythromycin). Side effects may include rash, nausea, stomach ache, diarrhea, loss of appetite, and vomiting.

Tetracycline is a category D drug in which fetal harm is possible. While not contraindicated for use, it should be avoided during pregnancy given the availability of other drugs able to treat the infection.

Prevention

Erythrasma is sometimes difficult to avoid if you live in a hot, humid climate where you are more likely to sweat. This is especially true if you work outdoors.

With that being said, bacterial colonization is less likely if you wash your skin regularly with an antibacterial soap or cleanser, paying extra attention to the groin, armpits, toes, and other areas where moisture accumulates. Always dry your skin thoroughly after bathing and change into fresh socks and shoes every day. If you are obese or unable to reach your toes for any other reason, ask a loved one to help or use a blow drier on a low setting.

You should also ensure that your shoes are completely dry before putting them on the next day, or alternate shoes so that they have time to fully dry.

If you are prone to sweating, an over-the-counter antiperspirant and foot product containing aluminum chloride (such as Gold Bond foot powder or ZeroSweat lotion) can often help. While some of the products can also be used on the groin or buttocks, be sure to read the product label or speak with your pharmacist just to be sure. In extra hot temperatures, try to use a fan or air conditioner while sleeping.

Weight loss should also be explored if you are not at a healthy weight. If you have recurrent bouts of erythrasma, speak with your doctor about a daily topical antifungal like Micotin (miconazole), which may help prevent recurrence without the risk of developing antibiotic resistance.

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