Is it permissible to use glycerin cream if one of its ingredients is a substance extracted from "animal brain," and the type of animal is not specified? And is it permissible to use other creams that contain glycerin with other substances?

If the animal substance in the cream is processed and transformed into another substance, there is no harm in that, because transformation purifies. However, if it was added before its transformation, then if it is from a marine animal or a slaughtered (halal) animal, there is no harm. Otherwise, it must be avoided, because the default ruling for meats and fats is prohibition until there is proof of permissibility. Creams with non-animal substances are permissible, unless their impurity or harm is known.