On group identities for the unit group of algebras and semigroup algebras over an infinite field

Let k be an infinite field. We fully describe when the unit group of a semigroup algebra k[S] of a semigroup S generated by finitely many periodic elements satisfies a group identity. This and some other recent results are proved by first showing that semiprime k-algebras generated by units are necessarily reduced whenever their unit group satisfies a group identity.