MayoClinic.com describes attention-deficit hyperactivity disorder (ADHD) as a common chronic neurobehavioral condition that is characterized by inattention, hyperactive and impulsive behavior. Children with ADHD may have a hard time making friends or doing well in school, while adults may have trouble maintaining relationships or keeping a job. The exact cause is unknown, but it has been suggested that biological factors triggered by environmental stressors may contribute to the development of ADHD.
Genetics
ADHD tends to run in families, according to the University of Maryland Medical Center. Twenty-five percent of people with ADHD have at least one close relative who shares the disorder. In addition, approximately one-third of all fathers diagnosed with the disorder during childhood have children who also display signs of inattention, hyperactivity and impulsivity.
Brain Damage
It has been suggested that injury or trauma to the brain can cause ADHD. Blows to the head, lack of oxygen, brain tumors, strokes or certain diseases can cause damage to a person's brain. A person with brain damage may develop ADHD because her brain can no longer regulate motor activity and impulses, according to the University of Maryland Medical Center.
Exposure to Toxins During Pregnancy
There appears to be a link between exposure of toxins during pregnancy and the development of ADHD, according to the MayoClinic.com. A mother's use of cigarettes, alcohol, cocaine or crack during pregnancy can prevent her baby's brain receptors from forming correctly, thus increasing the chance that her child will develop ADHD. In addition, fetal alcohol syndrome, or bacterial or viral infections during pregnancy, can increase the likelihood that the child will develop ADHD.
Brain Chemistry and Structural Differences
People with ADHD are deficient in the brain chemicals that are needed to inhibit impulses, coordinate thoughts and regulate behavior, according to the FamilyDoctor.org. Research suggests that people with ADHD have a low level of activity in the parts of the brain that control attention and motor activity. The National Institute of Mental Health states that people with ADHD tend to have less brain tissue in the areas of the brain that control attention than people who do not have the disorder.
