Men's shower gels and body sprays always smell horrible, consequently, I use ladies ones.
But why are they designated male and female? As far as I'm aware there's a glorious and inglorious history of perfumes being sought, manufactured and distributed by both men and women, going back around 4000 years.
My only guess would be its probably a combination of psychology (in the same way that pink is a 'female' colour) tradition and chemistry. There is the wide use of human pheromones such as Androstadienone in the manufacture of scents, however that link there also suggests that much is marketing bluster, as one would expect.
Its also interesting to note that the term Reverse Engineering also exists in the world of perfumery.