Have red dots in skin that appear in same spots. They itch and go away with Zyrtec (cetirizine). What could these be caused by?

Impossible to tell. It is impossible to tell what you have based on the scanty information. It may be from a drug reaction (fixed drug eruption) or even a form of mastocytosis but you really need to see your doctor about this if this has been bothering you.

Related Questions

I'm taking Zyrtec and it's important to me without it my skin itches and burns constantly. But it makes. My.stools yellow, any cause for concern?

Zyrtec. May cause diarrhea / cholestasis (no or less bile flow from bile ducts) which can cause light colored stools. You may want to change to another antihistaminic or hold the zyrtec, if you can, for some time, if the symptoms persist, see your doctor for evaluation of liver / gall bladder functions, best wishes. Read more...