The focus of preventive measures to date has been on the design of car seats, primarily through the introduction of head restraints, often called headrests. This approach is potentially problematic given the underlying assumption that purely mechanical factors cause<unk> injuries — an unproven theory. So far the injury reducing effects of head restraints appears to have been low, approximately 5–10%, because car seats have become stiffer in order to increase crashworthiness of cars in high-speed rear-end collisions which in turn could increase the risk of<unk> injury in low-speed rear impact collisions. Improvements in the geometry of car seats through better design and energy absorption could offer additional benefits. Active devices move the body in a crash in order to shift the loads on the car seat. For the last 40 years, vehicle safety researchers have been designing and gathering information on the ability of head restraints to mitigate injuries resulting from rear-end collisions. As a result, different types of head restraints have been developed by various manufactures to protect their occupants from<unk>  Below are definitions of different types of head restraints. Head restraint — refers to a device designed to limit the rearward displacement of an adult occupant's head in relation to the torso in order to reduce the risk of injury to the cervical vertebrae in the event of a rear impact. The most effective head restraint must allow a backset motion of less than 60 mm to prevent the hyperextension of the neck during impact. Integrated head restraint or fixed head restraint — refers to a head restraint formed by the upper part of the seat back, or a head restraint that is not height adjustable and cannot be detached from the seat or the vehicle structure except by the use of tools or following the partial or total removal of the seat furnishing". Adjustable head restraint — refers to a head restraint that is capable of being positioned to fit the morphology of the seated occupant. The device may permit horizontal displacement, known as tilt adjustment, and/or vertical displacement, known as height adjustment. Active head restraint — refers to a device designed to automatically improve head restraint position and/or geometry during an impact". Automatically adjusting head restraint — refers to a head restraint that automatically adjusts the position of the head restraint when the seat position is adjusted. A major issue in<unk> prevention is the lack of proper adjustment of the seat safety system by both drivers and passengers. Studies have shown that a well designed and adjusted head restraint could prevent potentially injurious head-neck kinematics in rear-end collisions by limiting the differential movement of the head and torso. The primary function of a head restraint is to minimize the relative rearward movement of the head and neck during rear impact. During a rear-end collision, the presence of an effective head restraint behind the occupant's head can limit the differential movement of the head and torso. A properly placed head restraint where one can sufficiently protect his/her head lower the chances of head injury by up to 35% during a rear-end collision. In contrast to a properly adjusted head restraint, research suggests that there may be an increased risk of neck injuries if the head restraint is incorrectly positioned. More studies by manufacturers and automobile safety organizations are currently undergoing to examine the best ways to reduce head and torso injuries during a rear-end impact with different geometries of the head restraint and seat-back systems. In most passenger vehicles where manually adjustable head restraints are fitted, proper use requires sufficient knowledge and awareness by occupants. When driving, the height of the head restraint is critical in influencing injury risk. A restraint should be at least as high as the head's center of gravity, or about 9 centimeters (3.5 inches) below the top of the head. The backset, or distance behind the head, should be as small as possible. Backsets of more than 10 centimeters (about 4 inches) have been associated with increased symptoms of neck injury in crashes. In a sitting position, the minimum height of the restraint should correspond to the top of the driver's ear or even higher. In addition, there should be minimal distance between the back of head and the point where it first meets the restraint. Due to low public awareness of the consequence of incorrect positioning of head restraints, some passenger vehicle manufactures have designed and implemented a range of devices into their models to protect their occupants. Some current systems are: * Mercedes-Benz A-Class Active Head Restraint (AHR), * Saab (Responsible for the first active head restraint), Opel, Ford, Nissan, Subaru, Hyundai, and Peugeot — Active Head restraint (SAHR), * Volvo and Jaguar —<unk> Protection System/Whiplash Prevention System (WHIPS), and * Toyota —<unk> Injury Lessening (WIL). The Insurance Institute for Highway Safety (IIHS) and other testing centers around the world have been involved in testing the effectiveness of head restraint and seat systems in laboratory conditions to assess their ability to prevent or mitigate<unk> injuries. They have found that over 60% of new motor vehicles on the market have "good" rated head restraints. Various organisations exist which list such vehicles
Whiplash 
Swayback
Sprain
Post-nasal drip
Tennis injuries
Factitious airs
Laryngospasm
Crossbite