M.I.
Hello,
My sister, dad, and I have all had similiar red, dry bumps on the backs of our arms. I don't know what exactly causes it but I know it is from having dry skin. I have found a GREAT lotion that has done wonders for this issue and any other dry skin or rashes. It's also great because this lotion does not contain any harmful chemicals that are found in some of the store brand cremes & lotions. You can get this lotion through a wellness company and I would be happy to share the full details if you are interested. Please feel free to contact me.
M. - www.livetotalwellness.com/freedom