The Dirty Leather Upholstery

Oils and Grease — Body oils can easily attach and transfer to the head cushions and armrests of your leather upholstery and can cause serious damage to the protective finishes found on leather.
Atmospheric Soils — Consider the dust that builds up on a coffee table or desk over a week. This same dust is being deposited on your leather. Additionally to this dust, you add airborne cooking oils and atmospheric pollution that is present, to some degree, in every home.
Common Soils — These soils include the common dirt tracked in from outside and garden by adults, kids and pets.
Dyes and Inks — The inks from newsprint in newspapers and from a leaky pen can readily be deposited on leather upholstery. Clothes such as denims can transfer dye onto leather in a process called dye transfer.