In an allergic reaction, the immune system starts fighting substances that are usually harmless as though these substances were trying to attack the body. This overreaction can cause a rash.
Contact dermatitis is a skin rash caused by something that touches the skin and makes it irritated and inflamed. Your skin may be red, swollen, dry, and may be cracked. Blisters may form and ooze. The rash will itch.