The design of U-shaped toilet seats in public restrooms is primarily for hygiene purposes. The American Standard National Plumbing Code, established in 1955 and later adopted by the Uniform Plumbing Code in 1973, requires water closets in public use to have open-front seats made of smooth non-absorbent material. This design reduces the surface area for germs to thrive and eliminates genital contact with the seat. It also allows women to wipe the perineal area without touching a potentially unhygienic surface. Various theories previously speculated on the reasons for this design, including cleanliness and fear of STIs.