The Green replacement discs are for people with normal or non-sensitive skin who have used the Pmd for several treatments and are ready for a level of exfoliation above the sensitive discs. Personal Microderm uses a patented spinning disc technology to deliver revolutionary microdermabrasion treatments and unmatched, brilliant results. The patented disc spins as it glides across the skin, providing brilliant results with each treatment. Aluminum oxide is a naturally occurring element that is extremely hard, second only to diamond. Aluminum Oxide crystals are non-airborne, hypoallergenic and antibacterial, which helps prevent any adverse reactions and reduce spreading of bacteria that may cause irritations.