[b112]

Animals also use things akin to soap. Birds love to bath in the ashes of a fire, the lye burns parasites, the dust chokes them.

I've watched many a bird do so, after a fire.

[AngryData]

Using ashes/lye directly on greasy human skin forms a primitive sort of soap too and isn't unheard of in human hygiene practices. And real fine dusts and grits in general seems pretty common as a method of hygiene for animals and humans alike.

[hypertele-Xii]

Some animals even rub themselves on ants' nests because formic acid kills bacteria.