When you fast, do not look gloomy like the hypocrites. They neglect their appearance, so that they may appear to others to be fasting. Amen, I say to you, they have received their reward. But when you fast, anoint your head and wash your face, so that you may not appear to be fasting, except to your Father who is hidden. And your Father who sees what is hidden will repay you.
(Matthew 6:16-18, NAB)