Good news: You don't have to abandon hair dyes and highlights throughout most of your pregnancy. Coloring agents can pass through the scalp and into your bloodstream, but in such minute quantities that they are generally thought to be harmless to a developing fetus. The data is limited but suggests that hair color doesn't cause birth defects or other problems -- even among people who work with it regularly, such as beauticians, says Dr. Koren. What's more, "you're not going to have many exposures during pregnancy," adds Zoe Diana Draelos, M.D., a dermatologist in High Point, North Carolina, who also studies cosmetics and skin medications. Still, due to the lack of direct data, Dr. Koren often advises women to avoid coloring their hair during the first trimester, when the baby's organs are developing.
Animal studies show that hair permanents and straighteners don't cause abnormalities in offspring, but there have been no studies involving people. "Research conducted in the 1980s suggests that people who work with products have higher rates of miscarriage, but the increase seems to be due to the physical aspects of the job -- such as standing for long hours -- rather than the chemical exposure," Dr. Koren says. More recently, researchers at the Centers for Disease Control and Prevention found that the risk of having a preterm- or low-birth-weight baby was no higher for a group of African-American women who had used a hair curling or straightening product during pregnancy or within three months of conceiving than for those who had not used these products.
Keep in mind, however, that pregnancy can make these hair treatments less effective -- and even a waste of money. "Hormones can do strange things," says Sandra Johnson, M.D., director of dermatology research at the University of Arkansas for Medical Sciences, in Little Rock. "You may not get the results you're used to."
But there may be another concern. In recent years some investigators and environmental groups have called attention to a class of chemical additives called phthalates, which are contained in many cosmetic products, including hair gels, sprays, and nail polish. Some phthalates have been linked to developmental problems in animals, especially to the male reproductive system, according to Jane Houlihan, vice president for research for the Environmental Working Group (EWG). A recent study from Columbia University confirmed that pregnant women are routinely exposed to these chemicals in the environment, and Italian researchers found that exposure appears to shorten pregnancy slightly.
Still, no one has linked a particular cosmetic or product to pregnancy problems or to abnormalities in newborns. "We have not had enough good solid research and data gathering," says Briggs. Tim Long, Ph.D., a toxicologist at Procter & Gamble, which makes scores of cosmetic products, argues that most contain only tiny doses of phthalates and an individual's exposure is minimal. "Many of the harmful effects these groups are citing come at extremely high doses," he says. Briggs agrees that while phthalates have suspected toxicity in humans, any potential hazard probably has more to do with repeated exposure (the chemicals are found in everything from medical devices to food packaging) than with the use of cosmetics alone. "They're so spread out in the environment," he says, "that they're hard to avoid."
If you want to steer clear of phthalates in beauty products until more is known, however, only use the products that the EWG has tested and found to be phthalate-free, such as Physique Extra Control Structuring Gel and Aussie Mega Styling Spray. (For a list, go here and here.)