This may sound strange but it is both the truth and strange. I have had a similar problem on various parts of my body. When I was in High School it was on the front of my thighs. Sometimes it would just be a rash and other times it would become very large and hard, a lot like a boil or pimple but would never really pop or drain, just sort of disappear. I have went to Doctors for about 40 years mainly for this problem in various forms and parts of my body. The thighs, then the middle of my back about 15 years ago and I was told it was shingles. About five years ago I started to get this very large painful grapfruit sized lumps and was told that I had a pylonital cyst. This is an ingrown hair that is usually in the rear around the anus. They would drain and was not very pleasant, so the Doctor told me to have it removed. They ended up taking out a football sized cyst and several smaller ones from my back or butt area. I started getting these things on the back of my neck behind my ears after the surgery and asked the Surgeon as they appeared to be related. She told me there was no way. Well, long story short, they were. I have had an injury when I was about 10 that for some reason made hair on my face grow between the layers of my skin. This produced this very sticky oily substance that when combined with the hair turned into this concrete. I had no feeling in a lot of places on my face because of this shell like growth. In a nut shell I have had this hair grown between my skin and have been spending every day since the surgery pulling it out! It sounds strange but is true. I have heard that they now have a name for this condition but it is very unusual. I went to Doctors for 40 years for this problem and not one Doctor would ever listen to me when I told them this condition. This will look like shingles, cold-sores and other similar outbreaks but for me it was this ingrown hair. I started to was my entire body with a good wash brusk or loupa, then when I was done, shave my entire body then run a pumus stone which seems to pick up these very fine hairs and helped quite a bit for my situation.