This level of pillow height is just right.

 

The height should be adjusted just enough to fill the space between the shoulders and ears.

There are various claims about the 'ideal' pillow, but there is no scientifically agreed-upon standard. However, experts consistently argue that the height of the pillow should be enough to fill the gap between the shoulders and ears. Professor Craig Hensley from Northwestern University Feinberg School of Medicine in the United States stated, "Filling the gap between the shoulders and ears naturally aligns the neck and spine," and added, "If the pillow is too high, it puts strain on the neck, and if it is too low, it puts strain on the spine."

A slightly firm pillow is better for the spine than an excessively soft pillow. Professor Rachel Salas of the Department of Sleep Neurology at Johns Hopkins University in the United States said, "A firm pillow protects the head and neck," and added, "However, if it is too hard, it can cause neck tension, so it is important to find a pillow with a moderate firmness." Among pillow types, latex is known to be the most helpful for restful sleep. Researchers at James Cook University in Australia investigated sleep quality based on five pillow materials: polyester, foam, contour foam, feathers, and latex. As a result, participants using latex pillows recorded the highest sleep quality, while those using feather pillows experienced symptoms such as headaches and stiffness upon waking.

If you wake up with a stuffy nose or frequently experience allergy symptoms, you should check the hygiene of your pillow. Pillows can be filled with skin flakes, dust, mold, and other allergens. Professor Salas said, "If you don't wash your pillow regularly, the trapped skin flakes, dust, and dust mites inside can interfere with sleep quality." The American Asthma and Allergy Foundation recommends replacing your pillow every two years. It is also advisable to wash pillowcases at least once a week. According to a survey conducted by an American mattress company, pillowcases that haven't been washed for a week contained approximately 17,000 times more bacteria than a toilet seat cover.