There are three main sleeping positions:
- On the back: Sleeping on one’s back, especially without a pillow, is the best position for the spine, as it allows the spine's natural curves to be accommodated (a small pillow under the knees helps maintain the natural curve of the body even better). In addition, it can help reduce acid reflux and there are even claims that it minimizes wrinkles. With a pillow under the head, however, the head and neck tend to be pulled forward, which can adversely affect breathing. It is therefore the worst sleeping position for those who are prone to snoring or sleep apnea. Two kinds of back sleeping positions are sometimes distinguished: "soldier" (with both arms pinned to the sides) and "starfish" (with arms positioned up and around the pillow).
- On the stomach: This is the worst possible position for those with neck and lower back problems. Even with only a thin pillow, this position flattens the natural curve of the spine, and also necessitates turning the head to one side which further distorts the alignment of the neck and spine. The pressure exerted on various joints and muscles, especially in the neck, can lead to irritated nerves and in turn lead to pain, numbness and tingling. Furthermore, the rib-cage is effectively trapped, and the internal organs (the lungs in particular) are restricted and put under undue pressure.
- On the side: Sleeping one one’s side is the most common position, and is generally good for overall health. It reduces snoring, and keeps the spine elongated. A thick pillow, especially a shaped one, is recommended to fill the space above the shoulders, so that the head and neck are supported in a neutral position. Shoulder and neck muscles can become constricted if the shoulder is positioned too high up towards the ear, and holding the hands or arms under the head should be avoided as it can stress nerves in the arms and lead to numbness. A small pillow between the legs may relieve any discomfort in the legs and lower back. Sleeping on the left side is recommended during pregnancy, but sleeping on the right side is preferable for overcoming hip and spinal concerns, reducing neck and back pain, minimizing acid reflux and reducing snoring. There are three types of side sleeping positions: "fetus" (lying on one side with the back curved and the limbs drawn in to the body - this is the most common single position, accounting for over 40% of all people, and twice as common among women as among men); "log" (lying on the side with both arms held against the body), and "yearner" (lying on one side with both arms stretched out in front).