Triclosan is a widely used bactericide, commonly used in soaps and other products. Smithsonian Magazine's science blog reports on new concerns about its safety:
Triclosan, A Chemical Used in Antibacterial Soaps, is Found to Impair Muscle Function
In recent years, though, research has shed light on a number of problems with employing triclosan so widely. Studies have shown that the chemical can disrupt the endocrine systems of several different animals, binding to receptor sites in the body, which prevents the thyroid hormone from functioning normally. Additionally, triclosan penetrates the skin and enters the bloodstream more easily than previously thought, and has turned up everywhere from aquatic environments to human breast milk in troubling quantities.
To this list of concerns, add one more: A new paper, published today in the Proceedings of the National Academy of Sciences, indicates that triclosan impairs muscle function in both animals and humans.
The effect wasn't just on skeletal muscle -- test on mice showed a reduction in heart function. In other words, we've been throwing a cardiac depressant into consumer products for years now. Since it has become pervasive in the environment, the researchers also tested its effect on fish; exposing minnows to triclosan was found to interfere with their ability to swim. (Usual disclaimers about animal research apply.)
According to the FDA, using tricolsan-containing antibacterial soaps has no benefits over washing with regular soap.