Genes. ADHD tends to run in families. Chemicals. Brain chemicals in people with ADHD may be out of balance. Brain changes. Areas of the brain that control attention are less active in children with ADHD. Poornutrition, infections, smoking, drinking, and substance abuse duringpregnancy. These things can affect a baby’s brain development. Toxins, such as lead. They may affect a child’s brain development. A brain injury or a brain disorder. Damage to the front of the brain, called the frontal lobe, can cause problems controlling impulses and emotions.