Dear customer, we apologize that the photo is a bit blur and we can't really conclude from photo the condition of the stain at the moment. A possibility could be oxidization. As the chain is made of alloy, though plated in white gold, we would recommend wearer try not have it in touch with substances which contain chemical (e.g. perfume, shower soap, moisturizer, etc.). otherwise, if it is only surface dirt, we do provide free polishing service at all our retail stores. We also provide after sales services like gold replating at a minimal fee. Hope these information helps.