Those yellow-brown shadows on an older mattress are sweat, body oils, and skin cells oxidizing over time. They are cosmetic but they also feed the odor and the mite population.
Home treatment
A light spray of dilute hydrogen peroxide with a small amount of dish soap, applied sparingly and blotted, lifts many sweat stains. Keep the mattress as dry as possible, saturation is the enemy.
Do not soak a mattress
Foam and inner padding hold water for days and can grow mold. Use the minimum liquid needed, blot aggressively, then dry with a fan and open window or AC running.
When to bring in extraction
Widespread yellowing across the whole sleeping surface will not respond to spot treatment. Professional extraction removes the salts and oils across the full surface and finishes with a deodorizer.
Bottom line
Add a washable protector after cleaning and the stains will not come back. Call for a mattress quote.
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