When you visit your doctor about a problem, your doctor needs to make sure that problem does not represent some sort of life threatening issue like cancer. When a physician evaluates a patient on the internet, there are not as many clues to go on to make that judgement so patients and physicians need to know when it is ok to make an educated guess and when you have to be sure of the diagnosis. A growth or a mole can always represent a skin cancer however a localized rash is rarely indicative of a serious medical condition.
The photo below was submitted by a young woman who thought she had ringworm. The doctor thought it looked more like nummular dermatitis but couldn’t be sure just from the photos. He reasoned that a trial of therapy with a topical steroid would not pose a risk of serious harm to the patient. If things didn’t clear, bringing the patient to the office for a KOH test could then be done. The rash cleared with triamcinolone 0.1% ointment.