Though some bed manufacturers guarantee their mattress for 20 years, is it still safe to sleep on a mattress that old? In many cases, it isn’t. Due to the fact that people often sweat while sleeping, moisture can get into the mattress. People also shed skin cells. In families with small children, the mattress may occasionally get urine on it. No matter how much you try to clean your mattress, those stains get embedded into the fabric and foam. The only answer is mattress replacement.