Just a note about hair dye.
Holly ea, bracci pm, hong mk, mueller ba, preston-martin s. West coast study of childhood brain tumours and maternal use of hair-colouring products. Paediatr perinat epidemiol. 2002 jul;16(3):226-35.
Found no evidence that hair coloring using n-nitroso compounds (noc) had increase in prenatal tumors.
(there was an 87 study that showed more use of hair color among women who ended up with kids with birth defects, but it was just one of many factors, and the above study ruled out the hair coloring as the cause).
There is lead in the dye, but while skin absorbtion of lead can happen, it is not that significant.
Now, the first trimester is always more risky for the development of the pregnancy, and in particular the first 40 days are very significant. So if women waith until 2nd month before dealing with any kind of chemicals, then the risk becomes even smaller. It is not clear that the risk is significant to begin with, though.