Triclosan is used in many personal care products as an anti-bacterial agent. You can find it in soaps, toothpaste etc. It is also an endocrine disruptor that effects at least two different (albeit interrelated) systems. Triclosan has some estrogenic effects. Paul et al. (Dec 2010) have demonstrated that triclosan alters thyroid hormone levels early in lactation. Thyroid hormones are especially important during fetal and infant development because they play crucial roles in brain development. Early thyroid hormone deficiency alters neurological function in animals, and in human, reduces IQ and increases ADHD-like behavior. There are many environmental contaminants that interfere with thyroid hormones including PCBs, PBDEs, perchlorate, and nitrate. It is difficult to study the impact of exposures to these chemicals in humans because its hard to know how much people are exposed to over time, and people are probably never exposed to just one agent at a time. Its important to consider additive (or synergistic or antagonistic) effects and not consider them individually. For now, its probably best for pregnant and lactating women to limit their exposure to triclosan. Thank you, Paul et al., for your hard work, and for fitting yet another piece into the puzzle. Here is the U.S. FDA's position on Triclosan safety.
as of today.
Paul KB, Hedge JM, Devito MJ, & Crofton KM (2010). Developmental triclosan exposure decreases maternal and neonatal thyroxine in rats. Environmental toxicology and chemistry / SETAC, 29 (12), 2840-4 PMID: 20954233