A recent report by The New York Times details what one physician referred to as an “astronomical” rise in the number of Attention Deficit-Hyperactivity Disorder (ADHD) diagnoses in children from preschool to high school age. Some in the medical community suggest that physicians are handing out ADHD diagnoses too easily—just as they are prescriptions for ADHD drugs—while others suggest that increased awareness of the disorder has led to proper diagnoses that might otherwise have been missed even a few years ago.

The report, compiled from new data released by the CDC, shows that one in five high school boys and 11% of all school-aged children in the U.S. have been diagnosed with the disorder. That’s about 6.4 million kids. The diagnosis rate has increased 16% just since 2007, and 41% in the last decade. Of those millions of kids diagnosed with ADHD, more than two-thirds of them take medication to treat the disorder, typically Ritalin or Adderall.

Read Related: Advocate for Your ADHD Child in School & Beyond

Even if some of these cases are exaggerated diagnoses, the report’s numbers still show a huge increase in ADHD, especially among high school boys. Frustrating about those numbers is the fact that doctors can’t point to a root cause of ADHD, though genetic and environmental factors are thought to have strong influence. While scientists more or less know how ADHD operates—the neurotransmitters that regulate behavior function differently in children with ADHD than with non-ADHD children, the question of “But why?” has yet to be answered.

Current science on ADHD suggests the following possible causes:

  • Prenatal & Postnatal Factors: Smoking and alcohol consumption during pregnancy are thought to increase predilection for ADHD, as does maternal infection during pregnancy, premature birth and low birth rate. Children who suffer traumatic brain injuries as infants or toddlers show a 30% chance of developing ADHD.

  • Environmental Factors: Lead exposure, now rare in the U.S. after bans on lead-based paint in 1978, is thought to cause ADHD. More recent thinking suggests that exposure to PCB (polychlorinated biphenyl) and pesticides increases the probability of developing the disorder. PCBs are used in a variety of industrial fluids and materials you probably wouldn’t want to expose your kids to anyway, but PCB is a pollutant that is widely dispersed in the environment, including in soil and drinking water.

  • Food Coloring: Kids love fancifully colored food, and some studies suggest that certain artificial food colorings increase the risk of developing ADHD. Though the FDA has yet to take action based on evidence it terms inconclusive, the European Union requires warning labels on all foods containing certain colorings because of their possible adverse effects on children, and has encouraged food manufacturers to voluntarily stop using the colorings.

  • Genetic Predisposition: If one or more family members, especially one or both parents, have ADHD, their children are far more likely to develop the condition.

  • Evolutionary Advantages?: Some theories suggest that ADHD is, or was, at least, evolutionarily beneficial, especially to males. Females seeking a mate might be drawn to the male seen as more likely to take risks and engage in dangerous behavior. We call that lack of impulse control, but our prehistoric ancestors may have seen these traits as conducive to survival, whether in hunting, exploring new areas, or defending against predators and enemies. In the developed world, lack of impulse control is less desirable, but even among modern nomadic peoples, men with ADHD exhibit better overall health.

  • Social Factors: The World Health Organization (WHO) cites studies that suggest that children who experience social trauma or upheaval are more likely to develop ADHD. These can include physical or emotional separation from parents, living in foster homes or orphanages, and when children are physically or emotionally abused.

Still other social scientists argue that ADHD is a social construct of doctors, parents and teachers, frustrated at their inability to manage children’s behavior. Thomas Szasz, a prominent humanist psychiatrist who died last year, was an outspoken critic of “mental illness” diagnoses, and claimed that mental/behavioral diagnoses, as well the as drugs to control these conditions, were an invention to try to control individuals whose behavior fell outside of societal norms. He claimed that ADHD was “invented and not discovered.”

With children now being born and raised in a very fast-paced world, and with early exposure to cell phones, computers, laptops and tablets, video games and of course, television, is hyperactivity and distraction the new norm? Or are some of these millions of diagnoses handed out to kids who just aren’t well-behaved, at home or in the classroom? Surely 6.4 million kids in the U.S. taking drugs for ADHD—which have their own undesired side effects—isn’t the answer. But until scientists can pinpoint the causes of ADHD, are we doomed to go from being the Prozac Nation to the Ritalin Nation?