Autism is a baffling disease that affects 500,000 children in the United States alone. Strangely enough, the incidence of autism has skyrocketed since the 1980s when only 1 in 10,000 children were diagnosed with the disorder, compared to 1 in 175 today. Scientists have yet to discover for certain what causes the disease, although there are several theories being discussed. The most controversial theory contends that mercury present in childhood vaccines may be one of the leading factors contributing to the development of the condition.

It is known that people exposed to methyl mercury, which is found in thermometers and polluted environments, have incurred damage due to contact. A mercury spill in Japan, for example, tainted fish in the area and caused those who ate the poisoned fish to develop Minimata disease. Another clue pointing to the dangerous effects of mercury exposure comes from an incident that occurred 100 years ago in the United States. Pink Disease (Acrodynia) was a mysterious illness that seemed to appear out of nowhere. The symptoms included social withdrawal and a deficiency of language skills. At the time, a particular type of teething powder that contained mercury was on the market - once it was taken off the market, this strange disease suddenly disappeared.

Those who believe in a link between mercury and autism cite the above as a few cases that may lend credence to the theory. Those studying the connection say that a combination of genetic susceptibility and exposure to mercury are most likely the two main factors that result in a child developing autistic disorder. For instance, it is not mercury exposure alone that causes problems, but rather, a minimum amount of exposure coupled with the child's decreased ability to excrete mercury properly.

Of course, this theory is a contentious one because childhood vaccines are being targeted as the main source of mercury exposure. A few years ago, most infant vaccines contained a preservative called thimerasol, which included ethyl mercury, although it is now being phased out of use. Although ethyl mercury is different than methyl mercury, in large amounts it can damage the nervous system. The hypothesis is, as children began receiving more and more vaccines over the years, they also received more mercury.

As with every controversial idea, not everyone agrees with this conjecture. The Centers for Disease Control and Prevention created two reports on the issue, both of which dismissed thimerasol as one of the causes of autism. And of course, many scientists and pediatricians are concerned fear will cause parents to avoid vaccinating their children.

In the end, no one really understands the root causes of autism, leaving many parents frustrated and without a valid explanation for the behavioral problems their autistic children experience every day. Hopefully, as more research is conducted, scientists will come closer to solving one of the world's most puzzling medical mysteries.