All of these factors make infants highly vulnerable to whiplash forces:

• A baby's head is large and heavy in proportion to his or her body. For this reason, when a baby is dropped or thrown, he or she will tend to land on his head.
• There is space between the brain and skull to allow for growth and development.
• Babies' neck muscles and ligaments are weak and not fully developed.
• An infant's skull is soft and pliable

When an infant or toddler is shaken, the skull is not yet strong enough to absorb much force. The force, therefore, is transmitted to the brain, which rebounds against the skull. This can cause bruising of the brain (cerebral contusion), swelling, pressure, and bleeding (intracerebral hemorrhage).

The large veins along the outside of the brain are also vulnerable and may tear with these injuries. Damage to these veins can lead to further bleeding, swelling, and increased pressure (subdural hematoma). This can easily cause permanent, severe brain damage or death.

Shaking an infant or small child may cause other injuries, such as damage to the neck, spine, and eyes. Eye damage is very common and may result in loss of vision (retinal hemorrhage).

Shaken baby syndrome is seldom an accident. The injuries are almost always caused by non-accidental trauma in other words, child abuse. An angry parent or caregiver may shake a baby to punish or quiet him or her. Many times they do not intend to harm the baby.

In rare instances, these types of injuries may be caused accidentally by actions such as tossing the baby in the air or jogging with the baby in a backpack. Shaken baby syndrome does not result from gentle bouncing or play.