There are several theories as to what can cause a fetish. Some people think fetishes stem from childhood. If there was an object or activity that became associated with masturbation or arousal, it could become a fetish for an adult. For example, if you watched BDSM porn with leather-clad dommes when you were younger, you might find yourself simply become aroused by leather in the future.

Another theory revolves around children who transfer feelings of unrequited love from their parents onto an object, resulting in a fetish. This is closely related to displacement in psychology.

The cause of some fetishes may be brain chemistry, which is invisible to the human eye and even difficult for scientists and doctors to understand. Some researchers believe that the reason why the foot fetish is so common is because of the areas in the brain that coincide with the genitals and feet are adjacent, and the wires get crossed.

Sexual obsession with feet could lead to an actual fetish of footwear or stockings. Interacting or even seeing shoes may arouse or may even be necessary for a person to become aroused and orgasm. In fact, some fetishes are so specified that it's the type of material (think leather or silk) that matters, while others only focus on the object itself.

There doesn't even need to be sexual contact for there to be a fetish involved. Fetishists may rub, sniff or otherwise handle their fetish object while masturbating. Some fetishists will also use the object to aid in masturbation or sex.