Many believe that vaccination is unnatural and weakens the body's immune system and should not be "played with". In 1998 a British study suggested that the MMR vaccine caused autism. They believed that the measles virus, once injected, made its way into the intestines and caused inflammatory bowel disease, which in turn caused developmental disorders such as autism. Some scientists have announced that many vaccinations contain both aluminum and traces of mercury, which when mixed together cause extreme synergistic toxicity. Parents against immunization believe that their children should rely on their natural immunity and argue that if every generation is vaccinated, every future generation will have no natural immunity. Many argue that as vaccine disease rates decline, chronic disease rates steadily increase due to reduced natural immunity resulting from vaccinations. The recent Bachmair study found a link between allergies and vaccination rates, where vaccinated children are twice as likely to suffer from allergies than unvaccinated ones. They are also 8 times more likely to suffer from it