A good way to steam clean a mattress at home is to use the upholstery attachment of a home steam cleaner or a rented professional steam cleaner. Because a wet mattress breeds bacteria, the mattress must be thoroughly dry before replacing the sheets.
The process for steam cleaning a mattress is similar to steam cleaning other upholstery. Use a vacuum cleaner attachment to vacuum the mattress first. Work slowly to remove as much dust and as many allergens as possible.
Apply the cleaning solution to the mattress. Avoid saturating the mattress, and test an inconspicuous area of a colored mattress for color steadfastness. Mix the cleaning solution according to the label, and spray it over the mattress. If needed, scrub the mattress gently with a scrub brush.
Use the steam cleaner's upholstery attachment to suction up the cleaning solution and dirt. Go over each section of the mattress carefully to remove as much water as possible. As with vacuuming, work slowly to allow the attachment to remove dirt and debris deep in the mattress.
Let the mattress dry completely before replacing the sheets. Use a fan directed toward the mattress to speed drying. If possible take the mattress to a clean location outdoors to let the sun and wind speed the drying process. Plan to steam clean the mattress on a warm, dry day to decrease drying time.