If you mean the dark ring or black buildup around a bathroom or kitchen faucet, it is usually caused by mildew, mineral deposits, soap residue, or grime trapped around the faucet base.
Try this first
Dry the area and wipe away loose dirt.
Soak a cloth or paper towel in white vinegar and place it around the dark ring for about 15–30 minutes. This can help with mineral buildup.
Scrub gently with an old toothbrush or soft brush.
Rinse with clean water and dry thoroughly.
If the discoloration is mold/mildew rather than mineral buildup, use a bathroom mold cleaner according to its label instead of vinegar.
If the ring is actually underneath the faucet
If cleaning doesn’t remove it, the seal or caulk around the faucet may have deteriorated and trapped moisture and grime underneath. In that case, the lasting solution may be to remove the old sealant, clean and completely dry the area, and reseal it with appropriate bathroom-grade silicone.
⚠️ Never mix vinegar with bleach or other cleaning products.
If you can send me a photo of the dark circle, I can tell you whether it looks more like rust, limescale, mildew, or deteriorated sealant and suggest the best way to remove it.
