Several environmental factors have been proposed to support the hypothesis that the actual frequency of autism has increased. These include certain foods, infectious disease, pesticides. There is overwhelming scientific evidence against the MMR hypothesis and no convincing evidence for the thiomersal (or Thimerosal) hypothesis, so these types of risk factors have to be ruled out. Although it is unknown whether autism's frequency has increased, any such increase would suggest directing more attention and funding toward addressing environmental factors instead of continuing to focus on genetics.