New mattresses need to be aired out for two reasons. First, there are odors remaining from the manufacturing process. (Manufacturers claim these odors are not harmful and will soon dissipate.) Second, additional odors are present from the plastic the mattress was wrapped in. Make sure to remove all plastic wrapping prior to the airing out.
The time it takes your mattress to air out may vary. Letting your mattress air out for 24 hours is recommended by the Sleep Products Safety Council. The best way to check if your mattress has aired out is to use your nose. If you are still bothered by the new mattress smell, let your mattress air out longer. Also, make sure you position your mattress in a manner that allows all sides to air out, not just the top. For example, lean the mattress against a wall.
Continue to let your mattress air out weekly. Turn the bed linens back for several hours one day a week. In addition, use a mattress pad to protect your mattress. Do not wrap your mattress in plastic as it stops air from circulating and can cause condensation to build up.