I've been thinking about this since you posted and still scratching my head (metaphorically.) I get PN itch occasionally but never a blister. Some years back I had an allergic reaction to mango and didn't realize it at the time. I managed to infect many body parts inadvertently. I had the same type of reaction you describes for 3 weeks intermittently without the blisters. Blisters makes me think it could be a form of the chicken pox virus. It's all I can come up with.