Yes, they can cause some injuries, especially in severe crashes. These injuries are usually limited to bruises and cracked collar bones and ribs - minor injuries in comparison to what often happens without the safety belt. It is important that safety belts be worn correctly to reduce the chance that they might injure you. Lap belts should be worn as low and snug as possible on the hips, since belts that are worn high crossing the stomach can cause injuries. Shoulder belts must also be worn snugly across the chest and middle of the shoulder. Never wear a shoulder belt with more than an inch of space between your chest and the belt.
Too much slack will allow your head to go too far forward in a front-end crash. If the shoulder belt rubs against your neck, try adjusting your seating position, the position of the seat or the seat belt height adjustment, if equipped, to get a proper fit. Cloth comfort sleeves may also be placed on the shoulder belt to make it more comfortable. Do not place the shoulder belt behind your back or under your arm. With the shoulder belt behind the back, your head and upper torso will be thrown forward in the event of a frontal crash. As with the belts behind the back, shoulder belts under the arm do not hold your head and upper torso back away from danger. In addition, the belt under the arm can fracture ribs and cause serious internal injuries.