If you are suffering anything from sleeplessness to back pain to allergies, the cause might be your mattress. Did you know it’s recommended that you replace your mattress every eight years? Why? Your mattress ages over time, and this leads to some serious issues. Here are three reasons why you’ll want to retire your old mattress now: 1. Mattresses Get Dirty One of the first things to happen to a new mattress is that it simply gets dirty. Over time, oils and sweat from our sleeping bodies will get into the mattress and sometimes even make it start to smell.