Have cystic like acne on back ever since getting allergy prick test done 2yrs ago? what could this be? how to cure? thanks!

Keloids: You may have developed keloids. Keloids can be considered to be "scars that don't know when to stop." a keloid, sometimes referred to as a keloid scar, is a tough heaped-up scar that rises quite abruptly above the rest of the skin. It usually has a smooth top and a pink or purple color. Keloids are irregularly shaped and tend to enlarge progressively. Unlike scars, keloids do not subside over time.