The maker of Dial Complete hand soap says that it kills more germs than any other brand. But is it safe?

That question has federal regulators, consumer advocates and soap manufacturers locked in a battle over the active ingredient in Dial Complete and many other antibacterial soaps, a chemical known as triclosan.

The Food and Drug Administration is reviewing the safety of the chemical, which was created more than 40 years ago as a surgical scrub for hospitals. Triclosan is now in a range of consumer products, including soaps, kitchen cutting boards and even a best-selling toothpaste, Colgate Total. It is so prevalent that a survey by the Centers for Disease Control and Prevention found the chemical present in the urine of 75 percent of Americans over the age of 5.

Several studies have shown that triclosan may alter hormone regulation in laboratory animals or cause antibiotic resistance, and some consumer groups and members of Congress want it banned in antiseptic products like hand soap. The F.D.A. has already said that soap with triclosan is no more effective than washing with ordinary soap and water, a finding that manufacturers dispute.