Back pain is caused by a variety of reasons. In a young person, the most common cause is bad posture. Reading in bed in an abnormal tilt of spine or working on a computer in an abnormal posture are the commonest culprits. Injuries are another reason for backache in the young. In developing countries tuberculosis of spine is something to look for. Finally malignancy of spine is also quite common in causing back pain.
In older people, injuries remain one of the most common reasons. The cushion between vertebrae (discs) become frail and tend to protrude in to the space between vertebrae leading to severe pain going down to lower limbs. An emergency may arise if urine retention occurs. In women infection of pelvis is a cause of chronic back ache. Malignancy is kept in mind in all cases.