In the 1950s it was generally agreed that nude photographs were not pornographic unless they showed pubic hair or, even worse, genitals. Respectable photography was careful to come close to, but not cross over, this line.
Penthouse published pictorials featuring visible female pubic hair almost from its inception in 1965. Playboy, however, showed a first slight glimpse of any pubic hair on Melodye Prentiss' centerfold (Miss July 1968), some 15 years after the magazine's introduction. With Playmates it was usually the case that the pubic area would be obscured by an item of clothing, a leg, or a piece of furniture. The first appearance of pubic hair in Playboy actually occurred in August 1969 in a pictorial featuring dancer/actress Paula Kelly. A few more glimpses of pubic hair appeared in some pictorials and centerfolds, but it wasn't until January 1971 when Liv Lindeland showed clearly visible pubic hair in her pictorial. The first Playmate to clearly have the first full frontal nude centerfold was Miss January 1972, Marilyn Cole. Incidentally, they both went on to become Playmate of the Year, respectively 1972 & 1973.
Eventually, the two magazines would move their content in opposite directions. Playboy positioned itself as the less explicit softcore alternative to be "read for the articles". Penthouse gravitated towards raunchier images, ultimately arriving at hardcore pornography and photographs of women urinating, in the late 1990s. Under new ownership in 2005, Penthouse began to steer toward a more softcore direction as well.