So basically I have had this rash off and on for years. It mainly starts showing up in hot weather. I have been to a specialized dermatologist to no avail. I have had two separate biopsies done, and nothing to show for it but two scars. Anything will help, even just ideas or thoughts. Much appreciated. Below is a link to a picture of similar rash. I haven't figured out how to upload my own pictures, so if someone wants to inform me I will be sure to upload my own photo.

Discovery Health "Understanding Skin Allergies: An Overview"

I have fair features and dry skin, so am prone to rashes of different types. I have had 'heat rash' which looks very much like the picture, and which I get when it's hot out and my clothes are too tight, not natural fabrics, are wool, are washed in scented detergent or too much detergent, or I get dirt/dust on my skin mixed with sweat.
For some people it's an allergy, perhaps to something outside, in which it falls under the general term of 'contact dermatitis.'

(I have also had cellulitis, which is a much more uniform red rash that spreads, nothing like your picture. It's caused by bacteria getting through a cut or bug bite. I also get intertrigo, a rash in folds of skin, under arms, etc, that is beet red and which can ooze. It can be caused by yeast or bacteria or fungus. I have been getting that since I had cellulitis 3 years ago.)
I doubt that you have anything but heat rash or possibly an outdoor allergy, from that picture! Can you tell us about any of the situations that I mention?