Avocados are known as one of the healthiest foods you can add to your diet. But in recent months, hospitals across the country have reported a shocking rise in emergency room visits linked to one simple mistake people make while preparing them.

Doctors are now issuing an urgent warning to every household.

It all comes down to a common injury known as “avocado hand.” Because of the slippery texture of the fruit and the pressure needed to remove the pit, people are accidentally slicing deep into their palms, fingers, and even tendons. Surgeons say the cuts are often so severe that some patients require stitches, nerve repair, or even surgery to regain movement.

Many of the injuries happen to completely healthy people who were simply trying to make guacamole, prepare a salad, or slice an avocado for breakfast. Hospitals have reported thousands of cases—enough to push medical experts to speak out and urge people to take the warning seriously.

What makes it worse is that the injuries are preventable. Safety experts now recommend a simple rule: never hold the avocado in your hand while removing the pit. Instead, place it flat on a cutting board and use a spoon to scoop the pit out. This eliminates the risk of the knife slipping through the soft flesh and into your hand.

For many families, this warning comes too late. But the hope is that spreading awareness now will keep more people from ending up in the emergency room over something as ordinary as preparing a piece of fruit.

A small change in how you cut an avocado could save you from a painful—and expensive—mistake.