I have suffered a myriad of chronic skin issues for decades. I’ve been treated for everything from acne to eczema to folliculitis with very little imorovement. Fast forward a bunch of years to after I started suddenly reacting to an odd assortment of foods and eventually found out about mcas, and I was finally able to tie alcohol, then nsaids and aspirin, and anti seizure meds (zonisamide) to my skin outbreaks. The key was that I had a huge skin reaction to mobic, and then I started having reactions within a few hours of having g alcohol, so I was able to identify the specific triggers. My spots are more like folliculitis, but on the mcas groups we have had numerous discussions of the weird skin presentations. Note that mcas folks can be sensitive to any med including antihistamines, usually from fillers and colors but also possible tO be sensitive to the actual antihistmine. In my opinion, it’s more likely you have some other chronic triggers happening and the zyrtec didn’t really have any part in it. For me, elimination of the triggers was the only relief, I was taking huge doses of antihistamines and using topical steroids with no affect.