People have a habit of bringing their phones to the bathroom. A three-minute trip to the throne can easily turn into 15-20 minutes of reading, scrolling and posting.

It might seem a harmless way to pass the time when you’re going number two. However, experts warn that what they call prolonged sitting on the toilet can harm your health. It’s even been connected to an increased risk of hemorrhoids and weakened pelvic muscles, said Dr. Lai Xue, a colorectal surgeon at the University of Texas Southwestern Medical Center in Dallas.

People should spend an average of five to 10 minutes on the john, according to Dr. Farah Monzur, an assistant professor of medicine and director of the Inflammatory Bowel Disease Center at Stony Brook Medicine on Long Island, New York.

Why is it a problem if you stay longer? First, here’s a short physics lesson. Gravity keeps us grounded on Earth, but that same gravity also forces the body to work harder to pump blood back up to the heart, Xue said.

The open oval-shaped toilet seat compresses the buttocks, keeping the rectum in a lower position than if you were sitting on the couch. With gravity pulling the lower half of the body down, the increased pressure affects your blood circulation.

“It becomes a one-way value where blood enters, but blood really can’t go back,” Xue said.

As a result, the veins and blood vessels surrounding the anus and lower rectum become enlarged and engorged with blood, increasing the risk of hemorrhoids.