I am selling these items because I have moved on from size M nipples. I used size M frequently (for Pigeon bottles). Sizes SS and S are relatively clean because I stopped using them quickly (for Pigeon bottles). The KR-100 is the same. (These are for newborns; I purchased them for sleep, but I preferred the regular type, so I only used them once or twice.) They have been sterilized, so please rest assured. Thank you.