Sterling Silver Rings Tarnishing

I bought 3 rings from Pandora which are sterling silver, but for some reason are tarnishing after wearing them for one day. They are turning black all over after one day of wear. They definitely do not come into contact with any chemicals (perfume, moisturiser, chlorine, hairspray, etc).
I have another ring from a less expensive brand that is also sterling silver, but I have worn it for 3 years with absolutely no issues. This ring does not tarnish and hasn't tarnished in the 3 years I've owned it.
The less expensive ring and the 3 pandora rings are exposed to the same elements, are taken off at the same time and are worn on my fingers for the same amount of time, yet the pandora rings all turn black after one day of wear.
I also have a tiffany and co bracelet that I have worn for 3 years also with no tarnishing at all. The bracelet is also sterling silver, and is never taken off at all, whereas I do take the rings off to shower and apply makeup.
I have come to the conclusion that the sterling silver pandora rings much be reacting with a chemical in my skin, but am unsure why my other ring and bracelet haven't tarnished at all over the 3 years of wear.
I was just wondering if anyone could let me know what specifically causes this blackening and why I am having an issue with pandora rings but none of the other items, even though they are all made from 925 sterling silver.
Thank you in advance :)

Dana ♥

The Centenary Diamond
my guess is that the ones that are tarnishing are not rhodium plated.

i used to have a roommate who could put on any non-rhodium-plated silver in the morning, and by lunchtime would have blackened the undersides where it touched her skin. any rings she slept in overnight would be heavily tarnished on the sides (between her fingers) in the morning.

it was purely due to her skin chemistry - and it was only silver that was not rhodium plated. she would also wear the plating off of costume jewelry almost as fast as i do, but in a different way.

it is pretty standard these days for a lot of sterling silver, and most white gold, to be rhodium plated, so if this bothers you i'd suggest stopping by your local jeweler and they should be able to rhodium plate the pieces. i am not personally familiar with Pandora, and do not know if they have any sort of warranty or intentional oxidation, but rhodium plating would likely invalidate the warranty and would definitely involve eliminating intentional, decorative oxidation.
It could also be that the pandora rings have more copper in them. If I wear my non plated (preferred) silver - it doesn’t tarnish...if I leave it sit on my will darken. That said - it can be caused by different skin chemistry too. My ears HATE sterling silver so I can’t leave silver earrings in long term or, even a full day. Lately, there is so much crap silver being made - stamped 925...that when I test it after receiving...IS NOT careful out there.
.925 silver then it is good, but if it contains more silver the more tendency to be black.Moreover some foods of our daily life have Sulfur and hydrogen - so they also turn black quickly.
I had read that the less alloys that are in the “mix” there would be less copper silver that was higher content than .925. For example .999 then the silver would tarnish less...I have a .999 wide silver ring that I have NEVER polished and is white and bright as the day I purchased it - it is not plated in any way. I have a .999 chain that has a bit of tarnish but nothing that it should have being as I have never cleaned that either. So, now I’m confused... can anyone chime in on this?:)