Your mattress is probably the one place you spend most of your daily time on. This means that over time things like dead skin cells and dust could pile up among the mattress fibres and make it one of the least clean items in the house. Dust mites that are an active cause of allergies actually feed on your dead skin cells and by not professionally cleaning your mattress you are creating a breeding ground for them right underneath where you or your children sleep.
It is a recommended practice to have both sides of your mattresses professionally cleaned twice a year but also carry out basic vacuum cleaning on both sides on a monthly basis to keep prevent the dust from piling up.