Shirt rubbed against arm as putting it on. Created red mark on arm and wont go away. After going in sun whole arm is red? Sun made skin feel prickly?

Sunburn. Some medications can make your skin more sensitive to sun exposure - ask your doctor if one of your medications could be causing this. Being exposed to enough sun will cause a sunburn. Skin sensitivity after sun exposure can also cause increased redness after mechanical trauma to the skin.