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Timing of Exposure

Research increasingly suggests that the links between chemical exposures and health outcomes are far more complex than traditional models portray. One emerging insight is that chemical exposures can have vastly different health impacts depending on the developmental stage when an individual is exposed (i).

Exposures during particular developmental stages, such as those that occur during puberty or prenatal development, may impact the long-term risks of developing cancer, neurological issues and reproductive challenges (ii). This may occur because of specific vulnerabilities during critical stages of development. For example, the brain is more vulnerable to chemical exposures during prenatal development and early childhood, and pubertal hormone levels may be disrupted by exposure to chemicals that mimic or disrupt the body’s own hormones. Exposure to hormone-disrupting chemicals early in life may have long-term impacts later in life that manifest as negative reproductive health outcomes or cancers of the breast or reproductive organs.

The Legacy of Human Exposures

Historical examples of toxic exposures in humans serve as inadvertent experiments that powerfully illustrate the ways that timing of exposure affects the development of disease. A key example is prenatal exposure to diethylstilbestrol (DES), a synthetic estrogen. DES was ineffective in its intended use of preventing miscarriage, yet led to serious health consequences. DES exposure led to structural abnormalities, infertility, and increased rates of vaginal and cervical cancers among the daughters of mothers who took DES during pregnancy (iii). In addition, research suggests an increased risk of breast cancer for both mothers and daughters (iv).

Many cosmetics contain chemicals that disrupt hormones in ways similar to DES. For instance, parabens (v), common preservatives in cosmetics, and triclosan (vi), a common active ingredient in antibacterial soaps and hand sanitizers, have been shown to disrupt hormones.

Another historical example of human chemical exposure illustrates that exposures may have stronger effects during puberty. A recent study found that exposure to DDT during childhood and adolescence led to increased risk of breast cancer before age 50 (vii). Exposure to endocrine-disrupting compounds in cosmetic products could lead to similar interactions between timing and exposure that increase health risks and outcomes in ways that may not be evident for decades.

More Information

Report: "Teen Girls' Body Burden of Hormone-Altering Cosmetics Chemicals"

i Gray, J (2008). State of the Evidence: The Connection between Breast Cancer and the Environment. San Francisco, CA: Breast Cancer Fund.

ii Antshel KM, Waisbren SE (2003). Developmental timing of exposure to elevated levels of phenylalanine is associated with ADHD symptom expression.Journal of Abnormal Child Psychology, 31(6):565-74.

Fenton SE (2006). Endocrine-disrupting compounds and mammary gland development: Early exposure and later life consequences. Endocrinology 147 (Suppl): S18-S24.

   Fenton SE, Hamm JT, Birnbaum LS, Youngblood GL (2002). Persistent abnormalities in the rat mammary gland following gestational and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-diosin (TCDD). Toxicological Science 67:63-74.

   Russo J, Hu YF, Silva IDCG, Russo IH (2001). Cancer risk related to mammary gland structure and development. Microscopy Research and Technique 52: 204-223.

iii Li S, Hursting SD, Davis BJ, McLachlan JA, Barrett JC (2003). Environmental exposure, DNA methylation, and gene regulation: Lessons from diethylstilbestrol-induced cancers. Annals of the NY Academy of Sciences.983: 161-169.

iv Colton T, Greenberg ER, Noller K, Resseguie L, Van Bennedom C, Heeren T, Zhang Y (1993). Breast cancer in mothers prescribed diethylstilbestrol in pregnancy. Further follow-up. Journal of the American Medical Association, 269: 2096-2100.
    Titus-Ernstoff L, Hatch EE, Hoover RN, Palmer J, Greenberg ER, Ricker W, Kaufman R, Noller K, Herbst Al, Colton T, Hartge P (2001). Long-term cancer risk in women given diethylstilbestrol (DES) during pregnancy. British Journal of Cancer, 84: 126-133.
    Troisi R, Hatch EE, Titus Ernstoff L, Hyer M, Palmer JR, Robboy SJ, Strohsnitter WC, Kaufman R, Herbst AL, Hoover RN. (2007). Cancer risk in women prenatally exposed to diethylstilbestrol. International Journal of Cancer, 121: 356-360.

v Environmental Working Group. Skin Deep. Ingredient Search for Parabens. Available online: Accessed August 21, 2008.

vi Environmental Working Group. Skin Deep. Ingredient Search for Triclosan. Available online: Accessed August 21, 2008.

vii Cohn BA, Wolff MA, Cirillo PM, Sholtz RI (2007). DDT and breast cancer in young women: New data on the significance of age at exposure. Environmental Health Perspectives, 115: 1406-1414. Available online: Accessed August 21, 2008.