Hair coloring is not allowed during late pregnancy. Because hair dyes are some chemical products and more heavy metals, such as mercury or lead, in the dyeing of hair will come into contact with the scalp, the capillaries on the scalp will inhale these harmful substances into the bloodstream, and then there is a possibility that they will enter the placenta, the growth and development of the baby to a certain extent. Most of the smell of hair dyes are more irritating, hair coloring time will be longer so that the long time to be stimulated by the smell, but also on the pregnant woman and the fetus may have adverse effects. For example, pregnant women have vomiting, nausea, coughing, allergic reactions and other symptoms. This stage of late pregnancy is best not to dye hair, usually also need to pay attention to regular pregnancy checkups, observe the development of the baby, there are abnormalities in time to intervene in the treatment.