KOH (potassium hydroxide) preparation. This test can help your doctor find
out whether a fungus is causing your rash. The doctor will take a sample of
your skin by lightly scraping the infected area. The sample is placed on a
slide with potassium hydroxide (KOH) solution and gently heated. If fungus
cells are present, the doctor can then see them with a microscope.
A Wood’s light exam. This test may be used to see if the rash is caused by a fungus. Your doctor will shine a special light on your skin where you have the rash. Certain kinds of fungi glow under this light.
A fungal culture (skin culture). This test can identify
the type of fungus that is causing your infection. Usually a culture is only
done if the diagnosis is difficult or the skin condition is not responding to
treatment. This test may take up to 4 weeks, because it takes time for the
fungus to grow.