Which of the following ingredients is linked to breast cancer?

Parabens are a class of preservatives commonly used in cosmetic and personal care products to prevent the growth of bacteria and mold. Research has indicated that parabens can be absorbed through the skin and have been found in human tissues, including breast tumors. The concern arises from parabens' ability to mimic estrogen, a hormone that plays a significant role in the development of breast cancer. Elevated levels of estrogen have been linked to an increased risk of breast cancer, leading to heightened scrutiny over the safety of parabens in products, especially those applied near breast tissue.

While other ingredients listed, such as 1,4 Dioxane, Selenium sulfide, and Phthalates, have their own concerns regarding health and safety, their specific association with breast cancer is not as clearly established as with parabens. This makes parabens the ingredient most closely linked to breast cancer in the context of this question.