What Causes Red Skin Rash With Specks On Arms And Legs?

I have a sort of blotchy rash, slightly raised, red, on my arms mostly but also with little dots all over my stomach and legs. I don t think that I ve done anything differently lately. Seems to have appeared out of nowhere. Sometimes itchy. Any ideas? I ve had it for about 3 days, no change even with antihistamines.