https://en.wikipedia.org/wiki/Potassium_alum

I find these sections of the wikipedia article amusing:

Alum may be used in depilatory waxes used for the removal of body hair or applied to freshly waxed skin as a soothing agent.

Potassium alum may be a weak irritant to the skin.

I guess it's a soothing irritant? Have you found it to be either soothing or irritating?