Polymer clay, much like wood or bone, is a porous material. As long as they are worn properly, infection can be avoided. Clay jewelry gets a bad reputation because of improper use such as not oiling before wearing, over wearing, and wearing in piercings that are not fully healed. If not baked thoroughly, moisture can resurface, making the jewelry even more porous and causing irritation. Like many other things in life, whether or not polymer clay is poor for your health is a matter of opinion and based off its user.