Skin rash that is itchy is usually due to allergies
. A simple rash is an inflammation of the skin (dermatitis). Contact dermatitis is caused by things your skin touches, such as
chemicals ( in elastic, latex, and rubber products), cosmetics, soaps, and detergents, dyes and other chemicals in clothing and plants like poison ivy, oak, or sumac.
If he can identify whether he has had contact with any of these in the recent past, then any one of these could have triggered this rash.