I slept on the same pillow for six years. It was flat, yellowed, and had approximately zero structural integrity. I just never thought about replacing it until my neck started hurting every morning and a physical therapist asked me what kind of pillow I used. I told her. She said, “That explains the neck.”

Side sleepers need height and firmness

When you sleep on your side, the space between your ear and shoulder needs to be filled completely. If the pillow is too low, your neck bends downward all night and you wake up with shoulder pain and a stiff neck. A firm, high-loft pillow four to six inches thick is the right range for most side sleepers.

Memory foam and latex pillows hold their shape better than down or polyester fill for side sleeping because they do not compress flat under the weight of your head. A contoured memory foam pillow with a higher side and a lower side lets you choose the best fit. They feel weird at first like sleeping on a sculpture but your neck adjusts within a few nights.

Back sleepers need medium support

Back sleepers need medium loft and medium firmness. Too high and your chin tucks toward your chest. Too low and your head tilts back. The pillow should support the natural curve of your cervical spine without forcing it into either extreme. A down-alternative or shredded memory foam pillow works well because you can remove or add fill to adjust the height.

I am mostly a back sleeper and use a shredded foam pillow with about a third of the fill removed. It took a few nights of tweaking to find the right amount, but now it conforms to my head and neck without pushing back. Most shredded foam pillows come overstuffed on purpose so you can customize them.

Stomach sleepers need almost nothing

Stomach sleeping is hard on your spine regardless, but using a very thin, soft pillow or no pillow at all minimizes the neck twist. A pillow more than three inches thick forces your neck into extreme rotation. A down or down-alternative pillow that compresses to near-flat is the best option for stomach sleepers who cannot break the habit.

If you wake up with lower back pain as a stomach sleeper, the pillow under your pelvis matters more than the one under your head. A flat pillow under your hips keeps your lower spine neutral instead of arched. Physical therapists recommend this constantly and almost nobody does it.

When to replace your pillow

The fold test: fold your pillow in half and place a shoe on top. If the pillow unfolds and throws the shoe off, it still has enough loft. If the shoe stays, the pillow is dead. Most pillows last eighteen to twenty-four months with regular use. If you wake up with neck pain that fades after being upright for thirty minutes, your pillow is the first thing to suspect.