About one-third of women in the United States dye their hair and most use a type of permanent color that does not require Food & Drug Administration approval. While the exact ingredients of hair dye and straighteners are unknown or listed on bottles, researchers noted hair products contain more than 5,000 chemicals, endocrine-disrupting compounds, and carcinogens potentially related to breast cancer. In addition, products used predominately by black women may contain more hormonally-active compounds that increase risk of breast cancer, researchers found.