Well over 50 percent of adult Americans dye their hair. Hair dyes painted on pregnant rats did not show any damage to their fetuses. Nevertheless, it is not recommended that women dye their hair during the first trimester. Some hair dyes contain heavy metals such as lead and bismuth, which can be absorbed though the scalp. These should be avoided during the first trimmest. It is probably less of a problem to highlight the hair using foil because such dye doesn’t touch the scalp at all.
Hair straighteners contain sodium hydroxide. Pregnant women should check the labels of hair products and avoid those that contain sodium hydrochloride. Pregnant women who want to straighten their hair should try hot-pressing or blow-drying it.
Hair permanents us ammonium and hydrogen peroxide solutions and should be avoided during the first trimester. Shampoos and vegetable dyes such as henna are considered safe for pregnant women to use.