Hi. Thanks for your query. Noted your history of age of 13, visiting beaches and have contact with sand, getting blisters on the scrotum and the anus area. The causes can be: Growing hair due to hitting puberty and hormonal changes can cause furunculosis. There can be reaction to something in the sand that can cause such a problems. Dand on the beach on its own can not cause such a problems. I would advise you the following in such a situation: Clean the area with liquid povidone iodine and apply every 6 hours to keep and maintain the area sterile. Oral antibiotics if need be or as advised by your Doctor whom you should visit for clinical evaluation and diagnosis and get a proper treatment based on a prescription.