Your complexion brightens. Metta shows in your face. As you practice metta, joy arises. At first it is barely noticeable, but as the joy increases, it begins to pervade your whole mind and body. Metta does not rely on any particular time, place, or condition. Once aroused, it can remain present in you the rest of your life. Your face cannot hide what is going on in your mind. When you are angry, it shows on your face. When you are peaceful, everyone notices. The energy of metta spreads through your bloodstream and nourishes your whole being. You look bright and clear, calm and peaceful.
(Read all eleven benefits at this link: https://tricycle.org/trikedaily/benefits-loving-friendliness-meditation/