break out in a rash
To experience visible skin irritation. After my husband broke out in a rash, we realized that the bushes he'd been trimming in the back yard were actually poison ivy. I had to go to the emergency room because the medication I'd been prescribed caused me to break out in a rash and have trouble breathing.
break out in a rash
[for the skin] to erupt with a rash. (See also break out in a cold sweat; (with a rash)">break out (with a rash).) I knew Dan had the chicken pox, because he broke out in a rash and had a dry cough. The baby breaks out in a rash all the time.