I recall hearing they used to occur in the old South, among African American females, as retaliation for taking someone’s man away. The acid used was lye, used in home-made soap making.
Lye (sodium hydroxide) is a base, not an acid.
Lye is a base (high pH), the opposite of an acid (low pH). Either an acid or a base can destroy tissue, though, if it’s strong enough.
Also used in disposing of bodies.