On what, then, do psychiatrists base their sweeping judgments? Most point to The Diagnostic and Statistical Manual of Mental Disorders — the fundamental handbook of psychiatry. Yet a glance at the manual reveals that the diagnostic criteria for shyness are far from clear. The third edition, which was published in 1980, said that a person could receive a diagnosis of what was then called “social phobia” if he was afraid of eating alone in restaurants, avoided public restrooms or was concerned about hand-trembling when writing checks.

The same guidelines could hardly apply to youngsters heading to kindergarten, children not yet potty-trained and toddlers just learning to eat. So in 1987, the revised third edition of the manual expanded the list of symptoms by adding anticipated concern about saying the wrong thing, a trait known to just about everyone on the planet. The diagnostic bar was set so low that even a preschooler could trip over it.

Self-help books and magazine articles further widened the definition of social anxiety disorder to include symptoms like test anxiety, aversion to writing on the blackboard and shunning of team sports. These ridiculously loose criteria led to more diagnoses, until social anxiety disorder in children began to look as if it were spreading like the common cold among second graders.

Then, having alerted the masses to their worrisome avoidance of public restrooms, the psychiatrists needed a remedy. Right on cue, GlaxoSmithKline, the maker of Paxil, declared in the late 1990s that its antidepressant could also treat social anxiety and, presumably, self-consciousness in restaurants. Nudged along by a public-awareness campaign (“Imagine Being Allergic to People”) that cost the drug maker more than $92 million in one year alone ($3 million more than Pfizer spent that year promoting Viagra), social anxiety quickly became the third most diagnosed mental illness in the nation, behind only depression and alcoholism. Studies put the total number of children affected at 15 percent — higher than the one in eight who psychiatrists had suggested were shy enough to need medical help.

This diagnosis was frequently irresponsible, and it also had human costs. After being prescribed Paxil or Zoloft for their shyness and public-speaking anxiety, a disturbingly large number of children, studies found, began to contemplate suicide and to suffer a host of other chronic side effects. This class of antidepressants, known as S.S.R.I.’s, had never been tested on children. Belatedly, the Food and Drug Administration agreed to require a “black box” warning on the drug label, cautioning doctors and parents that the drugs may be linked to suicide risk in young people.