About the material: We use 316L surgical stainless steel that is safe to the human body such as being used in medical equipment, but the gold, black, pink gold, etc. are coated with a color coating over surgical stainless steel. Therefore, we recommend silver color for those who have extreme metal allergies. In addition, colors other than silver may peel off and lose if left unused. We recommend that you do not leave it on and take care of it.