the first symptoms of guillain–barré syndrome are numbness, tingling, and pain, alone or in combination. this is followed by weakness of the legs and arms that affects both sides equally and worsens over time. the weakness can take half a day to over two weeks to reach maximum severity, and then becomes steady. in one in five people, the weakness continues to progress for as long as four weeks. the muscles of the neck may also be affected, and about half experience involvement of the cranial nerves which supply the head and face; this may lead to weakness of the muscles of the face, swallowing difficulties and sometimes weakness of the eye muscles. in 8%, the weakness affects only the legs (paraplegia or paraparesis). involvement of the muscles that control the bladder and anus is unusual. in total, about a third of people with guillain–barré syndrome continue to be able to walk. once the weakness has stopped progressing, it persists at a stable level ("plateau phase") before improvement occurs. the plateau phase can take between two days and six months, but the most common duration is a week. pain-related symptoms affect more than half, and include back pain, painful tingling, muscle pain and pain in the head and neck relating to irritation of the lining of the brain.