Hair treatments

OB/GYN News, Nov 1, 2003 by Gideon Koren

Women often have questions and concerns about the safety of hair treatments during pregnancy. The limited available data have not indicated problems with teratogenicity or other adverse reproductive outcomes associated with either occupational or personal exposure to hair dyes, permanent solutions, or other treatments such as straighteners.

That was our conclusion in a review that a colleague and I wrote in 1989 (JAMA 262[20]:2925, 1989). Since then, more studies have been published on this topic, but they do not alter our earlier conclusion.

Still, it is reasonable to advise women planning pregnancy to avoid hair permanents or dyes during the first trimester because of the paucity of direct information on the risks.

But this statement should not be interpreted to suggest that a problem exists. This distinction is particularly important for those exposed to these agents before they knew they were pregnant. There certainly is no indication that beauticians should stop working during pregnancy.

In vitro studies have shown that some of the compounds in hair products are mutagenic, but most have not been associated with birth defects in animal teratogenicity studies.

What needs to be considered is that exposure to these products is brief when they are used on the hair, and the effect of far lower concentrations is not clear. Quite a few of these products were tested in animal teratogenic studies and no problems were detected. These products have never been studied in humans in any organized manner. The studies included rodent studies, which found that topical application of dye formulations was not associated with toxic or teratogenic effects.

Another study of pregnant rodents found that different dyes administered by gavage caused no "biologically significant changes or defects."

These studies generally involved doses that were much greater than women would be exposed to with normal use of hair dyes.

Permanent wave products also were not teratogenic in animal studies, but again, there are no human data on exposure.

Two non-peer-reviewed studies commissioned by a beautician's professional association in the 1980s suggested that the rate of hypertension was higher among people working in this industry, and women tended to have more miscarriages and more preterm deliveries, but the rate of birth defects was not increased.

The miscarriage rate is more likely related to lifestyle or the physical part of the work rather than to chemical exposure on the job.

Several studies have been published recently on hair treatments and pregnancy. One evaluated whether exposure to chemicals used in hair curling or straightening products was linked to adverse birth-related effects. The case-control study of 525 African-American women compared cases--188 women with preterm births and 156 women with low-birth-weight babies--with 304 control women who delivered normal-birth-weight babies at term; the preterm and low-birth-weight groups overlapped (123 cases were both preterm and low birth weight).

The risk of having a preterm or low-birth-weight baby was actually lower among women who had used a chemical hair straightener or curler during pregnancy or within the 3 months before conceiving, indicating that other confounding variables could not be controlled in this study (Am. J. Epidemiol. 149[8]:712-16, 1999).

In 1997, a large, retrospective Dutch cohort study compared reproductive disorders in hairdressers with those in clothing sales clerks between 1986 and 1988 and between 1991 and 1993.

Among women who conceived during the earlier period, the risks of spontaneous abortion, prolonged time to pregnancy, and low-birth-weight infants were higher among the hairdressers. These risks were not increased among hairdressers during the later period, indicating that the risks were decreasing with time.

During both periods, major malformations were more common among the infants of hairdressers, but the numbers were small and should not be over-interpreted, the authors said (Epidemiology 8[4]:396-401, 1997).

A large case-control study on the risk factors for brain tumors among children diagnosed between 1984 and 1991 found no evidence that the use of hair dyes during pregnancy was associated with a greater risk of childhood brain cancer among offspring (Paediatr. Perinat. Epidemiol. 16[3]:226-35, 2002).

Although a greater risk was associated with a single use of a hair dye the month before conception, and with exclusive use of semi-permanent dye during the month before pregnancy and/or during the first trimester, the confidence interval for these two associations "was imprecise and the estimate was not different from unity.'"

In summary, hair treatments have not been associated with increased teratogenic risk, but it is reasonable to suggest to women that they minimize hair treatments during the first trimester due to the paucity of data.

There is no reason for alarm if a woman continued hair treatments before she knew she was pregnant.

DR. GIDEON KOREN, professor of pediatrics, pharmacology, pharmacy, medicine, and medical genetics at the University of Toronto, holds the Research Leadership in Better Pharmacotherapy During Pregnancy and Lactation. He is director of the Motherisk Program (www.motherisk.org), a teratogen information service at the Hospital for Sick Children, Toronto.