When personality quirks start to get in the way of a person's productivity and quality of life, they may be the sign of a serious mental health disorder.

Behaviors such as attention problems, repetitive actions, and obsessive thoughts may signal several different conditions whose symptoms often overlap. While only a doctor can diagnose the actual root of these issues, here are a few of the most common causes.

Obsessive compulsive disorder (OCD)
For people with full-blown OCD, this chronic anxiety disorder can be downright disabling: They become plagued by persistent, unwelcome thoughts—such a something bad happening to a loved one—and feel that the only way to prevent these thoughts is to engage in rituals such as repetitive hand washing or checking door locks, for example.

Body dysmorphic disorder
Sufferers of this condition obsess about a perceived flaw in their physical appearance, like moles, freckles, scars, acne, or body hair. People with the disorder frequently check themselves in the mirror, avoid having their pictures taken, and repeatedly check, touch, or measure the imagined flaw.

This intense preoccupation with physical health can cause sufferers to worry that minor and imagined physical symptoms are signs of a serious illness. They aren't reassured when tests or doctors' diagnoses come back negative. Read one writer's experience with hypochondria.

People with trichotillomania have an irresistible urge to pull their hair from their head, eyebrows, or body. Pathological skin picking (also called neurotic excoriation, psychogenic excoriation, and dermatotillomania) is similar.

Tic disorders
This group of disorders includes Tourette syndrome, in which sufferers make impulsive sounds or movements—like blinking their eyes or shrugging their shoulders—over which they have little control. Although Tourette syndrome may be best known for the uncontrollable tendency to blurt out curse words or other inappropriate words or phrases, this symptom (called coprolalia) actually occurs in only a small number of patients.

Attention deficit hyperactivity disorder (ADHD)
This condition is often misdiagnosed, especially in adults, because patients do not in fact have to exhibit symptoms of hyperactivity. Some adult ADHD sufferers can appear quite laid back, even lazy or lethargic, and without the ability to stay focused on important tasks. Instead, people with ADHD often "hyperfocus" on, or become obsessed with, trivial project details or hobbies.