It seems to be a new thing, but I can’t wear anything higher up on my neck without getting a rash now. Whether it’s a necklace or even a scarf, etc. The skin there is just hyper-sensitive. So strange.Oh no sorry to hear you have allergies with the metal! Did you figure out a way to wear them without getting a rash? As for the onyx, using their cleaning cloth really does nothing but push the dirt and oils to the edges so I don’t even bother using it. You could use mild soapy water and rinse it well, then dry it off with a microfiber towel and make sure to get the corner edges.
I wouldn’t use a toothbrush on the stone, it might cause some micro scratches on the surface if you scrub too hard. A microfiber towel should suffice after you rinse off most of the grime and dirt.
I haven’t worn it yet at the new length (and my WG MOP one should be back soon too), but am hoping with the motif sitting on my clothes, and just a small part of the chain on the skin that it’ll be ok. (hopefully

Thank you for the tip about avoiding the toothbrush. I’ll work on it with a microfiber cloth.