925 silver does oxidize!
The oxidation process of silver is something very normal because 
when it comes into contact with oxygen, air and environmental
humidity, it turns yellow and then turns black. Also if 925 silver
comes into contact with materials containing sulfur it can trigger
this process more quickly.
It is worth noting that not all 925 silver pieces go through this
process in the same way or at the same time, as there are external
factors that can intervene or favor this, such as the pH of the
skin, the water, the products of beauty that we use, where we keep
it, etc.
However, 925 silver is a super noble material that, despite being 
oxidized by any external factor, can return to its original state
with a simple cleaning process. In the next few days we will be
uploading an article on the blog on how you can do it.
I hope that this article has clarified your doubts in relation to
this noble material such as 925 silver. This will always be the best
option to make your jewelry purchases.