Unfortunately, doctors/scientists do not really have an answer to your question yet. The symptoms of ADD have become well recognized and described (inattention, lack of focus, sometimes hyperactivity), but researchers are still not sure of the exact cause. At the moment, most research suggests some neurobiological reason --> meaning, the chemicals and nerves in the brains of people with ADD, behave a little differently than in non-ADD people.

ADD may be genetic because some families seem to have a high number of ADD people. Some people have suggested that diet and family environment may lead to ADD, but most research indicates that these causes are unlikely.

The good news is that ADD is now widely recognized, so people who have it can get the medical and phsychological help they need to lead normal and productive lives.

There are many hypothesis as to what causes Attention Deficit Disorder (ADD). The most prominent is that ADD is genetic. That is, if one of your parents has it, then you are at a 25% chance to have ADD.

Another hypothesis is that multimedia such as television, internet, and video games are involved with ADD. The idea behind this hypothesis is that these different forms of stimulation inundate the brain and result in a short attention to one media channel. You can image switching your attention from instant messaging to email to television, you get the picture.

Fundamentally, behavior elicited by ADD has something to do with changes in the brain. I read a recent study that mentions some shampoos as being implicated risks for pregnant women. Shampoo and other preservatives are said to cause nerve cells not to grow correctly, which causes neurological disorders.

Nobody knows for sure what causes ADD, or even how to accurately diagnose this condition. ADD is probably caused by a chemical imbalance in the brain--either too much or not enough of some specific chemical, possibly a neurotransmitter. We don't know for sure, though, and it's very difficult to test for some of these brain chemicals.

Some researchers want to split the condition into two different ones: ADD and ADHD (attention deficit hyperactive disorder), because some people with ADD are also hyperactive but some are not. Since many other conditions, like sleep disorders and depression, can have symptoms just like ADD, many people get mis-diagnosed. And since we don't know for sure what causes the condition, treating it is difficult. Different treatments work differently in different people--even people who definitely have ADD, not some other condition.