Question: "Is it a sin to have a sexual fetish?"
Answer: A sexual fetish is usually an interest in a particular part of the body, feet for example. Fetishes range from an attraction to an absolute obsession. The question arises, then, is it wrong to have a sexual fetish? The answer depends on the status of the person asking the question and the extent to which the sexual fetish is practiced.
There is nothing wrong with finding a particular part of the body especially attractive. The Bible says that our bodies are fearfully and wonderfully made (Psalm 139:14). Within the confines of marriage, there is nothing wrong with a husband and/or wife particularly enjoying a part of their spouse's body. While some fetishes seem very strange, there is no body part that is "off limits" between a husband and wife, within the "mutual consent" concept (1 Corinthians 7:5). Within a marriage, a sexual fetish would only become sinful if it became an obsession (an idol), or if the fetish bothered the spouse or in any way went against his/her will. Please read our article on "What is a Christian couple allowed to do in sex?"
For an unmarried person, again, it is not wrong to have an attraction to a particular part of the body. The unmarried person, though, needs to be especially careful that the attraction does not turn into lust. As soon as the attraction turns into a desire to do something immoral, it has become sin. An attraction to the opposite sex is normal and natural. Again, attraction is not the issue. But as Jesus said, "You have heard that it was said, 'Do not commit adultery.' But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart" (Matthew 5:27-28).
Certain fetishes seem exceedingly strange to some people. At the same time, within the confines of a mutually consenting marriage, it is not wrong to have a sexual fetish. The key is avoiding obsession, lust, and making the spouse uncomfortable. For the unmarried, a sexual fetish should be suppressed as much as possible. Something as harmless as an attraction to feet can turn into lust, which can turn into sexual immorality. Romans 6:19 says, "Just as you used to offer the parts of your body in slavery to impurity and to ever-increasing wickedness, so now offer them in slavery to righteousness leading to holiness."