Like the title says. And notice there is nothing here about this Allergy. Strange?
Allergies to polyester and other synthetics is called Allergic contact dermatitis.
Does this make it any easier to believe or absorb?
Here is a link to 1000's of picture of it. Look through these until you find one like yours. Remember it looks a little different on everyone. Find a pic of the same body area as you have issue with too.
http://www.dermnet.com/Allergic-Contact-Dermatitis/photos/1