Bed pillows provide a space for dust, dirt and dust mites. While pillow slips are frequently changed, the pillow itself is not, so allergens can collect and cause problems. Given that we lay our heads on these pillows, it makes it easy to inhale the allergens. Pillows made of hypo-allergic material (no feathers or down) do not provide the kind of environment preferred by dust mites, so that problem is dramatically decreased or eliminated.