Fungal scalp infections are diagnosed after a visual inspection of the scalp and observation of symptoms; scraping may be taken to confirm the diagnosis in a laboratory setting, according to eMedicineHealth. An examination using ultraviolet light is sometimes useful in spotting a certain ringworm or fungal species, although the species is not as common in the United States as it once was, so this diagnostic technique is rarely still used.
Scrapings of the scalp in the affected area are used for microscopic studies. A surgical blade is usually used to scrape the area to obtain a sample for study, although a toothbrush run over the scalp, cotton swabs or moistened gauze may be used instead. After a sample has been collected, a solution of potassium hydroxide is added to a slide smeared with the specimen and observed under a microscope. The presence of fungal spores can yield a positive diagnosis, although it is only effective around half the time.
A culture of the specimen leads to a more definitive diagnosis. This method involves collecting the scrapings and placing them in a medium that serves as food for the fungi. If growth takes place, then fungi are present. It can take up to 10 days to make a diagnosis using the culture method.