All types of pornography are harmful to a couple's sex life.
That was the conclusion reached by researchers at Brigham Young University in Utah, who studied 3,500 people who were in relationships.
The study published in the Journal of Sex Research found that people who are in a relationship and usually watch pornography alone are more likely to be less stable in their relationship and feel less satisfied with it.
"Couples should know that pornography is a risk factor in their relationship," the report said.
Study leader Brian J. Willoughby, a professor at Mormon University's School of Family Life, told KSL news agency.
"It is not only "hard" pornography that leads to negative results," he emphasized.
Of the 3,500 people surveyed, 72% were heterosexual, 17% homosexual and 11% bisexual. Additionally, 55% of participants were married, 23% reported living with their partner, 12% remarried, and 2% reported being in a relationship.
The study then divided pornography into two categories: "mainstream," where sex is consensual between couples or individuals, and "hard," where sex involves acts that are more violent and depict non-consensual behavior.
The researchers found that there was no difference between the types of pornography in terms of producing negative affect:
"All types of pornography made people feel more unstable and less satisfied with their relationship."
According to Willoughby, men, especially those who are religious, were more affected by pornography. Willoughby and other researchers hypothesized that the reason the study affected religious men so strongly was because viewing pornography conflicted with their moral beliefs and thus they were in a "conflict."
According to Willoughby the reason why pornography affects couples so much is because they enter into the process of comparing themselves to other men and women, creating unrealistic expectations of themselves, their bodies and who they think they should be.