Worse odors are usually mold spores in the woodwork or plasterwork.
A paint called KILZ in Home Depot or a paint store usually covers it up. If the odor smells like sewerage, it may be that you have a hole or crack in a stack that vents the toilets. We have this problem in our house, and the smell comes and goes. We are taking bids on getting it fixed by plumber. Probably at considerable expense.