Cleaning your mattresses & sofas should be on your deep cleaning schedule (i.e., at least twice a year). The average human sheds a whole layer of skin in one month. These skin cells can make your mattress smell and look dirty, not to mention the spills, sweat and allergens like dirt, pollens and bacteria that can get onto the mattress. Another factor to consider about your mattress is dust mites. These mites are not visible to the human eye and feed on dead skin cells within your mattress. However, for many people, dust mites are problematic because of allergies.