Flake was not the right word to use, but the fine powders of cosmetics can cause a very fine dusting of the gold to come off when the powder is in-between the skin and the ring.
Rusty, sorry I did not know......
Spinach, liver, beans, pumpkin seeds, oysters, mussels, clams, shrimp, sardines...
Could be a possibility of cosmetics coming into contact with the gold and forming an abrasive layer next to the skin; this can cause the gold to flake off.