I would go with food grade mineral oil or unscented baby oil. It's about as safe as you can get, to loosen it up and wipe it off with some tissue or cotton. Then there's no risk of fingernail damage. You can find food grade mineral oil wherever you find bamboo kitchen utensils, usually cutting boards - you oil the wood to keep it from drying out and cracking, so the oil has to be safe to get on your food. =)