The Pickling Lime reacts with acids, so you don't want to accidentally inhale any because it might cause a burning sensation in your sinus or your eyes. I handle the powder on my skin all the time with no problems. It's possible people with very acidic, sensitive skin may notice irritation when it comes in contact with sensitive, moist skin.
Remember to always dilute 1 Tablespoon with a gallon of distilled water and shake before use.