Bleachers are typically unprotected from the sun. Thus, the benches are subject to "bleaching" from  solar radiation. Some claim that the term was derived from that feeling of being bleached by the sun while sitting in them. Open seating was originally called the "bleaching boards" as early as 1877. By the early 1900s, the term "bleachers" was being used for both the seating area and its occupants.