Acids can burn and eat away any material.
Acids hold a position of being dangerous.
Sure enough a drop of concentrated hydrochloric acid can damage any surface or burn your skin.
But there are many acids that are very gentle and are a part of various nutritious foods.
One such food stuff is Apple!
It contains malic acid- which pretty much does not cause any harm to us.
Similarly vinegar is an acid, which is added to many cuisines and doesn't cause any harm to us.