Alopecia areata. Dysregulation of certain immune cells results in a completely bald patch that appears suddenly. The area could remain bare for weeks or months. Waiting for a while, or injection of a dilute cortisone suspension were the most common treatment options. Three sessions of PRP has shown success in treating alopecia areata. Here is a link to an article that can be viewed on www.pubmed.gov : http://onlinelibrary.wiley.com/doi/10.1111/dth.12437/full .