Passengers also can carry on liquids and gels in any quantity that they buy in airport shops after passing through security, including at duty-free shops. Drinks and other items are screened before being sold in secure airport areas.
Testing by the FBI and at government labs showed that small containers of liquids "don't pose a real threat," Hawley said.
Jim Kapin, head of health and safety for the American Chemical Society, said small quantities of liquids could not seriously damage an airplane. Even if several terrorists smuggled liquid explosives on board, it is "practically speaking, impossible" to make a bomb on an airplane because of the equipment and expertise required, Kapin said.
The TSA banned liquids and gels from carry-on bags Aug. 10 after British authorities reported foiling a plot to destroy U.S.-bound airplanes using liquid explosives. The ban led millions of passengers to check luggage rather than try to carry bags on.
"The total ban is no longer needed from a security point of view," Hawley said. "It doesn't make sense to have our (screeners) fishing out lip gloss and mascara."
The Homeland Security Department is no less concerned about liquid explosives, and is keeping in place the heightened security alert that began Aug. 10 for aviation, said Michael Jackson, department deputy secretary.
Easing the ban was hailed by the Air Transport Association, an airline trade group, and the National Business Travel Association. Some airlines reported a loss of business since the liquid ban took effect.
"This is going to make life easier for thousands of business travelers who have been forced since Aug. 10 to check bags on short business trips," said Caleb Tiller of the travel association.
The amount of checked luggage has increased 20% nationwide since Aug. 10. That has strained TSA systems that screen bags for bombs. Hawley had feared screeners might "cut corners" to keep up with extra bags but said Monday the "system is working OK now."
Jackson said allowing liquids in carry-ons will "release a little pressure there."
Hawley said he does not expect the change to lengthen lines at security checkpoints. "People will be well-ingrained" in what they can bring on airplanes, Hawley said.
A.J. Castilla, a screener at Boston's Logan International Airport and spokesman for a screeners union, said the new policy "is more confusing and certainly will add to the lines during the holidays."
"We're just adding another level of screening to a screening process that was simple," Castilla said.
Travelers must remove the bags that hold liquids from their carry-ons so they can go through X-ray machines separately and be inspected by screeners. Each traveler may carry only one bag, which can hold several 3-ounce containers.