The phrase "bad rash" refers to a skin condition that causes irritation and redness on the skin, often accompanied by itchiness and discomfort. Full definition
Our son gets bad rashes and the warmth of the wipe really helped. (babycenter.com)
Three weeks ago I started getting a very bad rash on my face and neck. (bodyunburdened.com)
I used to be able to drink and then many years ago, I brand of champagne gave me very bad rashes and ever since I've been getting rashes with alcohol. (glamdevils.com)