A tanning agent is a substance used to darken the skin, usually through exposure to sunlight or artificial light. The two crossword solutions for the term 'tanning agent' are SUN and SUNSHINE. SUN is a 3-letter word that refers to the star at the center of our solar system, which emits ultraviolet radiation that can be used to tan the skin. SUNSHINE is an 8-letter word that refers to the direct rays of the SUN, which can also be used to tan the skin.