It seems hard to go wrong with a hand soap that "kills 99 percent of germs" it encounters. But critics of anti-bacterial soaps in the home say there's plenty to be concerned about.

A government advisory panel will take a look at that Thursday.

The popularity of soaps and other products claiming anti-bacterial properties skyrocketed in the last decade as consumers turned to them as a defense against household illnesses. But some people contend that a number of the products, particularly those that use synthetic chemicals rather than alcohol or bleach, pose the risk of creating germs that are resistant to antibacterials as well as antibiotics.

Those critics say antibacterials are no more effective than regular soap in reducing infections and illnesses. The Food and Drug Administration (search), in briefing documents posted on the Internet ahead of Thursday's hearing, said the agency has not found any medical studies that definitively linked specific anti-bacterial products to reduced infection rates.

Unlike anti-bacterial products, regular household soap helps separate bacteria from the skin so they wash down the drain or attach to the hand towel when hands are dried. Anti-bacterial soap kills the bacteria outright.

Manufacturers disagree with many of the critics' claims, while both sides point to studies they say support their point of view. An FDA panel of independent experts will take up these concerns in a public hearing.

The Nonprescription Drugs Advisory Committee (search) will consider whether there is evidence that these products pose long-term hazards, as the critics contend. They can make recommendations on the sales and labeling of these products to the FDA, which ultimately has the authority to restrict availability of such soaps and related items.

The FDA briefing documents do not suggest any such ruling is imminent.

Critics like Dr. Stuart Levy, president of the Alliance for the Prudent Use of Antibiotics (search), say these products should be banned for use in healthy households. Instead, he says, keep them where they are needed: in hospitals and in homes with very sick people at greater risk if they get a bacterial infection.

"We run the risk of changing the kinds of bacteria we confront every day in the home," said Levy, a professor of medicine and molecular biology at Tufts University School of Medicine (search).

Here's how, he says: The small percentage of bacteria that survive a brush with the soap may develop resistance to it. What's more, he says, some surviving bacteria may have an improved ability to pump out all threatening substances, including antibiotics used to cure infections.

Those survivors may pass that mutation to their offspring, and the adaptation can come to dominate an entire population of bacteria, creating a resistance.

While Levy says that has happened in lab studies, there's no firm evidence it's happening in households. Brian Sansoni, spokesman for The Soap and Detergent Association (search), an industry group, said studies have found no link between the real-world use of anti-bacterial products and bacterial resistance.

"These products are proven to provide a preventive benefit for their users," Sansoni said.

A recent study published by the Centers for Disease Control and Prevention, in which scientists observed the development of bacteria in 224 households for a year, showed no significant increase in resistant bacteria in houses using anti-bacterial instead of regular soap. Nor did it show that anti-bacterial soap led to healthier homes than regular soap.

It called for further studies, saying the effect could take place over a longer term. Levy is listed as one of the study's authors.

The FDA, in briefing documents, said "current data are conflicting and unclear" on this issue.

Last month, the agency began enforcing the first U.S. ban of a veterinary antibiotic because of concerns it could lead to antibiotic-resistant bacteria in humans.

Other issues to be considered by FDA panelists include whether the synthetic chemicals in some soaps pose a hazard in the environment after they wash down the drain and through wastewater systems.

They also will look at whether the use of antibacterials in homes may in fact leave those homes too clean for young children, who may need some exposure to the bacterial world to develop a strong immune system.

This controversial theory, called the "Hygiene Hypothesis," suggests that growing up in a too-clean environment may cause a person to develop asthma and serious allergies later in life.