Definition of "hives"

So when I was diagnosed with a fairly difficult-to-treat disease called idiopathic angioedema and chronic urticaria (a fancy way of saying we don’t know why you swell and hey, enjoy the 24/7 hives) six months ago, I wasn't quite sure how to cope.

2014 January 20, Simona Supekar, “How the Internet Helped Me Cope With My Rare Disease”, in The Atlantic‎

When she recovers enough to look down at her arms [...] she blinks to see them covered in faint, but rising, puffy welts. Hives. She's breaking out in hives.

2020, N. K. Jemisin, The City We Became, Orbit, page 108