Remove all linens from the mattress.
Take the mattress outside on a warm, sunny day. Allow the mattress to lean up against a pole or wall. Make sure to lay some newspapers or sheets under the mattress to protect the mattress from dirt.
Spray the mattress with a fabric odor remover. Make sure to spray thoroughly until it is slightly damp.
Allow the mattress to dry in the sun. Move the mattress back inside after it dries.
Sprinkle baking soda directly onto the mattress. Allow baking soda to sit overnight. Vacuum baking soda.