It's a condition that can make leaving one's house a terrifying ordeal. Asking someone out on a date can induce panic attacks. And the thought of speaking up in class or at a meeting can be so frightening that sufferers will try to avoid the situations entirely. It's called social anxiety disorder or social phobia, and while often debilitating—a new survey underscores its harmful effect on relationships—it's treatable.

At times, the disorder is difficult to distinguish from normal shyness, and some experts claim it's overdiagnosed and overtreated. Most estimates place the number of Americans with social phobia at about 15 million, but critics counter that those estimates include many people who are merely shy, not sick.

Puzzlingly, people with social anxiety are often gregarious and outgoing individuals—in certain contexts. Many have little trouble interacting with close friends and family in familiar settings. But when they are taken out of this comfort zone, their reactions can take a damaging toll on their relationships, education, and careers. "Those with social phobia tend to marry later in life, if at all, and regularly have trouble dating for fear of embarrassment," says Jerilyn Ross, president of the Anxiety Disorders Association of America.

The April survey, which Ross's association conducted among 287 people with the disorder, found that 35 percent thought their social phobia caused them to avoid intimacy with their partners. Yet it also highlighted the benefits of getting help: After receiving treatment, 59 percent reported improvements in their romantic relationships. Other research has found that socially phobic people tend to avoid participating in classroom activities and may drop out of school or college entirely. Many are underemployed and may even forgo career advancement if it means assuming public speaking roles or managing other employees.

As with many psychological conditions, the symptoms of social phobia lie on a spectrum of severity. Some people experience the anxiety only in specific situations—talking on the phone, for example, or using a public restroom. Others have a more generalized phobia that makes most kinds of human interaction stressful. Still others may be comfortable onstage and yet have trouble with one-on-one encounters. Some sufferers even have physical symptoms, including severe blushing, hand tremors, dizziness, excessive sweating, and heart palpitations, says Ross.

Paralyzed. At the heart of the condition, say experts, is not merely shyness but a paralyzing fear of humiliation or being judged negatively as boring or unintelligent. A shy person will eventually acclimate to an anxiety-inducing situation. Someone with pathological and pervasive social anxiety will not.

Such fear of stumbling socially or embarrassing oneself in front of others may not be entirely unfounded, a recent study suggests. Researchers found measurable deficits in social interaction when subjects with social phobia were asked to hold one-on-one conversations. On the other hand, the study, published online in the February edition of the Journal of Anxiety Disorders, also found that the same people tend to overestimate their shortcomings when giving a speech or performing in front of a crowd.

Some experts contend that the definition of social anxiety disorder is overly broad, sweeping up those with normal personalities and rational fears. Northwestern University research Prof. Christopher Lane, for example, says the line between shyness and social phobia should be drawn to "limit diagnosis to those chronically impaired." In his book Shyness: How Normal Behavior Became a Sickness, Lane argues that psychiatrists and drug manufacturers have inflated the disorder's prevalence.