You can carry that toothpaste on board once again

Starting today, travelers can again put shampoo, toothpaste and other liquids and gels in their carry-ons and take them through airport security checkpoints — but only in containers of 3 ounces or less and only if they're in clear, zip-top plastic bags.

Travelers also will be able to buy beverages and other liquids and gels at shops inside airport security checkpoints and carry them on board.

The Transportation Security Administration announced the new rules Monday.

TSA chief Kip Hawley told a news conference at Ronald Reagan Washington National Airport that the changes, which he described as a "common-sense approach," will "keep us at a high level of security but make it a little bit easier for passengers."

Severe restrictions on carry-on items were imposed Aug. 10 after British authorities announced they had arrested a group of suspected terrorists who they said were plotting to blow up U.S.-bound flights with liquid explosives.

"We now know enough to say that a total ban is no longer needed from a security point of view," Hawley said, citing explosives experiments done by the FBI and other laboratories.

Under the new rules, travelers will be required to put the toiletries in a single clear, quart-sized, zip-top plastic bag and place the bag in a bin to be X-rayed separately, as is required for laptops.

Carry-on rules

What you can take on: Travel-size containers (3 oz. or less) of toiletries; larger sizes of medicines; beverages purchased inside the airport security zone.

How to pack it: Travel-size toiletries must be packed in a single quart-size, clear, zip-top plastic bag. (Pack larger sizes in checked luggage.) Medicines must be declared at security.

Want to know more? Read all the rules at www.tsa.gov

Although the X-ray machines can't identify whether a substance is an explosive, they can pick out anomalies that may indicate a substance is intended for use in a bomb, the TSA said. The agency is testing new equipment that can detect explosive substances at checkpoints, Hawley said.

Larger amounts of prescription liquid medications such as diabetic glucose treatments, infant formula and nonprescription medicines such as cough syrup and contact solution will also be allowed in carry-ons. They won't have to be put into plastic bags, but they must be declared at the checkpoints for additional screening.

Liquids and gels brought to the airport in containers larger than 3 ounces are allowed only in checked baggage.

Drugstores sell 3-ounce sample sizes of many travel toiletries, but travelers can put their liquids in any type of container as long as it's not bigger than 3 ounces, said Jennifer Peppin, a TSA spokeswoman in Seattle.

"You can't take 3 ounces of liquid and put it in a 4-ounce bottle," she said.

Peppin said screeners have been trained for the changes, but some predicted initial confusion.

"All this raises the outlandish scenario of TSA screeners playing Solomon and deciding what is or isn't a 3-ounce portion and whether a particular plastic bag is too large to be allowed," Joe Brancatelli said in an e-mail to subscribers to his business travel newsletter, JoeSentMe.com.

Sea-Tac spokesman Bob Parker said there could be delays at checkpoints until passengers get used to the new rules. "We think it's a real positive, but it's still a change and any change in the screening process can cause problems for a few days," he said.

Sea-Tac advises travelers to arrive at the airport two hours ahead of their flights.

Caleb Tiller, a spokesman for the Virginia-based National Business Travel Association, said business travelers were pleased by the changes. The previous rules "caused some frustration for business travelers who typically, especially on short trips, would not want to check bags," Tiller said. "If the ban stayed in place long-term, it could have a negative impact on travel."

The association, which represents 2,700 corporate travel managers, had been urging the Homeland Security Department and the TSA to ease some of the restrictions, he said.

Despite the relaxed rules, the government threat level for domestic and international flights remains at "orange," indicating a high risk of terrorist attack, said Michael Jackson, deputy secretary of Homeland Security. "We don't anticipate changing that overall aviation threat level anytime in the near future," he said.

One former Homeland Security official questioned the rationale behind the announcement.

"I think TSA bowed to pressure from the public and industry," said Clark Kent Ervin, the department's former inspector general. "Either harmless liquids and gels can be used to make a bomb or they can't be. If they can be, and we still have no defenses against it, it is as dangerous to let them onto airplanes as it is to let pre-fabricated bombs."

Carol Pucci: 206-464-3701 or cpucci@seattletimes.com

The Associated Press and Los Angeles Times contributed to this report.