Black eyes, bruises and broken bones heal, but when teens fight, intelligence might take the longest to recover.

Criminology researchers say adolescent boys who are injured in two fights lose about as many IQ points as students who miss an entire year of school.

For girls, similar cognitive losses occur after only a single fight.

The researchers looked at information gathered from middle school and high school students 1994 and 2002 through an initiative called the National Longitudinal Study of Adolescent Health.

More than 20,000 students were tracked from their youth to early adulthood in efforts to learn about personality traits, relationships and other behaviors.

Investigators from Florida State University examined the data to see whether teens who received injuries in fights displayed decreases in intelligence.

All fighting injuries that sent students to a doctor or nurse for treatment were included, with head injuries lumped in with all other types of trauma.

Meanwhile, a method called the Picture Vocabulary Test was used at various points during data collection to measure verbal IQ.

After analysis, the researchers connected lower performance in the IQ tests to fighting, saying boys lost one-point-six IQ points for each fight, while girls lost an average of three points.

The researchers say the drop in scores was roughly equivalent to losses that occur from missing a single year of school.

More research will determine whether head injuries pack a bigger cognitive punch than injuries elsewhere in the body.

Likewise, the next round of investigation may reveal whether injuries from contact sports are as apparently detrimental to intelligence.

But early indications say when it comes to fighting, intelligence takes a hit.