Without closer examination of the ‘peeling’ of the product, it is not easy to comment on how the material has these scratches. The lid is made of polypropylene (PP) which may be subject to peeling/ scratches due to rough surface contacts.
As heat treatment from the sterilizer is being used, there may be the softening of the PP material and any friction applied to it may have caused the peeling phenomenon.
Every user’s experience of the product varies due to the different intensity and frequency of sterilization. Nonetheless, we would like to reassure you that the peeling does not affect the main function of the bottle. Meanwhile, we would definitely recommend that you make a replacement of the collar/ teat.
Moving forward, for care tips we would recommend using baby bottle brush as the bristles are designed to be gentle on all the bottle parts. If a bottle brush is not used, the kitchen sponge may cause peeling due to the abrasion during washing.
Also, do use undiluted bottle detergent when washing so that you wouldn’t have to scrub too hard to remove any milk residue.
Other than that, we would highly encourage you to remove all items from the sterilizer after a cycle of sterilization has been completed and gently “press to close” when assembling the bottles.