Complex regional pain syndrome type 1 (CRPS 1) is a chronic pain condition that usually affects one limb (arm, leg, hand, or foot) after an injury or trauma to that limb. It is characterized by intense burning pain, swelling, and changes in skin color, temperature, and/or texture. It can also cause stiffness, muscle spasms, and changes in nail and hair growth. CRPS 1 is believed to be caused by damage to the peripheral and central nervous systems. Treatment typically includes physical therapy, medications, nerve blocks, and other interventions.