Why is my mattress yellow?

A yellow mattress is most often caused by body oils, sweat, and moisture soaking into the mattress fabric and upper foam layers over months or years of use.

Foam mattresses also yellow on their own as polyurethane and memory foam oxidize with age and light exposure, even when kept clean. A mattress without a protector or a mattress with poor airflow shows discoloration faster, and spills or humidity can add visible stains on top of the gradual aging.

Polyurethane and memory foam mattresses yellow through oxidation as the foam ages, separate from any sweat or stain damage.
Body oils and sweat soak into a mattress cover and comfort layers, leaving yellow patches where sleepers lie.
Most mattress owners are advised to replace a mattress after roughly 7 to 10 years, when aging becomes visible.
Light yellowing alone does not mean a mattress is unsafe; it signals age, moisture exposure, or staining.