Dust Mite Allergies affect tens of thousands of people in the UK alone, and are one of the most common allergies we get asked about here at Breathing Space. The dust mite itself is not the allergen, believe it or not it is dust mite's faeces which contain the actual allergen ( known as DerP1 ) and causes the allergic reaction. When you walk across the floor in your home, you unwittingly disturb these faeces and grind them into a fine dust which floats up into the air and becomes ripe for inhalation. These fine dust particles are so small they actually can pass through many Hepa filter type air purifiers. This is why and Airfree air purifier which actually destroys ALL particles no matter how small, is absolutely the most effective air purifier to buy if you suffer from dust mite allergies.