Most herniated disks occur in your lower back (lumbar spine), although they can also occur in your neck (cervical spine). The most common signs and symptoms of a herniated disk are:

• Arm or leg pain. If your herniated disk is in your lower back, you'll typically feel the most intense pain in your buttocks, thigh and calf. It may also involve part of the foot. If your herniated disk is in your neck, the pain will typically be most intense in the shoulder and arm. This pain may shoot into your arm or leg when you cough, sneeze or move your spine into certain positions.

• Numbness or tingling. People who have a herniated disk often experience numbness or tingling in the body part served by the affected nerves.

• Weakness. Muscles served by the affected nerves tend to weaken. This may cause you to stumble, or impair your ability to lift or hold items.

You also can have a herniated disk without knowing it — herniated disks sometimes show up on spinal images of people who have no symptoms of a disk problem.

Disk herniation is most often the result of a gradual, aging-related wear and tear called disk degeneration. As you age, your spinal disks lose some of their water content. That makes them less flexible and more prone to tearing or rupturing with even a minor strain or twist.

Most people can't pinpoint the exact cause of their herniated disk. Sometimes, using your back muscles instead of your leg and thigh muscles to lift large, heavy objects can lead to a herniated disk, as can twisting and turning while lifting. Rarely, a traumatic event such as a fall or a blow to the back can cause a herniated disk.

Factors that increase your risk of a herniated disk may include:

• Weight. Excess body weight causes extra stress on the disks in your lower back.

• Occupation. People with physically demanding jobs have a greater risk of back problems. Repetitive lifting, pulling, pushing, bending sideways and twisting also may increase your risk of a herniated disk.

• Genetics. Some people inherit a predisposition to developing a herniated disk.

Your spinal cord doesn't extend into the lower portion of your spinal canal. Just below your waist, the spinal cord separates into a group of long nerve roots (cauda equina) that resemble a horse's tail. Rarely, disk herniation can compress the entire cauda equina. Emergency surgery may be required to avoid permanent weakness or paralysis.

Seek emergency medical attention if you have:

• Worsening symptoms. Pain, numbness or weakness may increase to the point that you can't perform your usual daily activities.

• Bladder or bowel dysfunction. People who have cauda equina syndrome may become incontinent or have difficulty urinating even with a full bladder.