Toxicokinetic Profiles and Potential Endocrine Disruption Effects at the Reproductive Level Promoted by Siloxanes Used in Consumer Products.

Siloxanes, commonly known as silicones, are polymeric compounds made up of silicon and oxygen atoms bonded together alternately. Within this group of substances are linear methyl-siloxanes and cyclic methyl-siloxanes, with octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) being the most produced and used industrially. Due to their versatility, high production volume, stability, and local presence in environmental matrices and biological fluids such as breast milk, fat, and plasma, siloxanes have been considered persistent organic pollutants, representing a public health problem. This represents a public health concern, especially when different investigations have reported potential endocrine effects at the reproductive level in experimental animals exposed to D4 and D5. The objective of this study was to review the potential reproductive and endocrine effects derived from siloxanes present in personal care products (PCPs). The results of the literature review confirmed that D4 and D5 were the most used siloxanes as additives in PCP because they improve the emollient properties of the cosmetic and the physical appearance of hair and skin. Similarly the toxicological effects of siloxanes, particularly D4, D5, and D6 included significant endocrine disruption, reproductive toxicity, and liver toxicity. Studies in SD and F-344 rats, commonly used to assess these effects, have shown that D4 has low estrogenic activity, binding to ER-α receptors, whereas D5 does not bind to estrogen receptors. D4 exposure has been associated with increased uterine weight and estrous cycle alterations, leading to prolonged exposure to estrogens, which raises the risk of endometrial hyperproliferation and carcinogenesis. Recent research highlights that D5 exposure disrupts follicle growth, endometrial receptivity, and steroidogenesis, resulting in infertility and hormonal imbalances, potentially causing disorders like endometriosis and increased cancer risk. Chronic exposure to D5 has been linked to the development of uterine endometrial adenocarcinoma, with higher doses further elevating this risk.