Pseudo-Chrysostom
Catena Aurea · Matthäusevangelium 6
But thou, when thou fastest, anoint thine head, and wash thy face; That thou appear not unto men to fast, but unto thy Father which is in secret: and thy Father, which seeth in secret, shall reward thee openly.
Therefore the simple interpretation of this is, that is added as an hyperbolical explanation of the command; as though He had said, Yea, so far should ye be from any display of your fasting, that if it might be (which yet it may not be) so done, ye should even do such things as are tokens of luxury and feasting.