I obviosuly can't be sure, but I can say this:
1. Things that come and go aren't usually very serious. Thinsg that come and stay, or spread, are more worrisome.
2. Linear rashes are often assoicated with
externalExternal incontinence devices trauma, like scratching. You may have dermaographism ("skin writing.") This refers to welts that appear when the skin is scratched or rubbed, when histamine leaks out of mast cells in the skin and produces short-lived hives.
Here's how to check: take an unopened pen and make a design on the skin-- an X or a square. See if that leaves a red trail of the same shape. If it does, that's your answer.
No treatment is needed. The body just goes through a phase like this once in a while, but it doesn't mean anything.
If you can't reproduce the marks this way and they persist, photograph them and show a doctor.
Best.
Dr. Rockoff