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Do I have ringworm or pityriasis rosea?

Found this reddish pink patch on my leg that my doctor doesn't know what it is. Said it could be ringworm or pityriasis rosea but we're treating it like ringworm. What is the difference between these things?
This is an issue to discuss with a dermatologist. Pityriasis rosea is a rash without a clear-cut known cause; most dermatologists believe a viral infection may be the culprit. Typically the rash begins with the appearance of a "herald patch" that signifies the appearance of the classic pityriasis rash one to two weeks later. The herald patch is red and can be very similar in appearance to a ringworm infection. Usually this patch occurs on the abdomen, but can occur anywhere. The subsequent rash consists of oval-shaped red/pink patches that spread over the torso and back. Ringworm, on the other hand, is a superficial fungal infection of the skin. It is also known as tinea corporis when it appears on the body, and tinea pedis when it occurs on the feet (athlete's foot). It typically manifests as a circular red and scaly patch on the skin, usually with a central clearing. A generalized rash as a result of ringworm does not occur in people with normal immune systems. To help tell the difference between a ringworm infection and a pityriasis herald patch, a scraping of the rash can be examined under the microscope. When scrapings from a ringworm are examined under some drops of potassium hydroxide, fungal elements can be seen to confirm the diagnosis. Again, please see your dermatologist soon.
This answer is for general informational purposes only and is not a substitute for professional medical advice.
If you think you may have a medical emergency, call your doctor or (in the United States) 911 immediately. Always seek the advice of your doctor before starting or changing treatment. Medical professionals who provide responses to health-related questions are intended third party beneficiaries with certain rights under ZocDoc’s Terms of Service.

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