The phrase "itchy rash" refers to a red and bumpy skin condition that makes you feel like scratching it because it is very irritating and causes discomfort. Full definition
The horse coat is very short and many people are sensitive to its texture, developing itchy rashes within minutes of contact. (vin.com)
This type of itchy rash usually shows up where you came into contact with something you're allergic or sensitive to, be it a chemical, paint, wool, or a fragrance. (health.com)