bumps and a painful stinging sensation.

have several bumps on my upper arm that, on occasion, create a painful stinging sensation. Each is smooth, raised about 1/8" and 1/84" to 3/8" in diameter. The first one developed about 25 years ago, developed into 3 about 15 years ago and now I have 6 in that general location. The pain started within the past year or so and I have not been able to pinpoint any irritant or trigger. They are not blisters (as in herpes). They are not attractive and I would like to identify then to see if there is a treatment.