It's basically citric acid one of the two acids safe for re-passivating stainless steel the other being nitric. I did get some on my anodized toe rail and noticed no ill effects. It does nothing to gelcoat and I prefer not to get any acid on Awlgrip though I have gotten SS on my Alwcraft 2000 finish and not seen any signs of etching. Again this is a mild acid and why it takes a long time to work but it really works well and also protects it well.