The shoes have to be placed on an X-ray belt for screening before passengers can put them back on.
Later Sunday, the Homeland Security Department reduced the threat level for U.S.-bound flights from Britain from red, for "severe," to orange, for "high." All other flights operating in or destined for the United States remain at orange.
"The security measures already taken have allowed us to address an imminent threat of attack for flights between the United Kingdom and the United States," Homeland Security Secretary Michael Chertoff said in a statement. "Let me be clear: This does not mean the threat is over. The investigation continues to follow all leads.
"In particular, we are remaining vigilant for any signs of planning within the U.S. or directed at Americans," Chertoff said.
The eased restrictions on medicine and the mandatory shoe removal were among several measures the Transportation Security Administration ordered Sunday in response to the thwarted terror plot in Britain involving U.S.-bound airplanes.
TSA had previously banned all liquid medications; now it will allow up to 4 ounces of liquid nonprescription medicine.
The alleged conspirators had planned to blow up as many as 10 planes flying from Britain to the U.S. using liquid explosives, which TSA's security equipment can't detect in carryon luggage.
In other measures, TSA said it would let flyers carry on low blood sugar treatments including glucose gel for diabetics; solid lipstick; and baby food. But it said all aerosols are prohibited.
On Saturday, the TSA added mascara to the list of banned items, which includes baby teethers with gel or liquid inside, children's toys with gel inside and gel candles.
But CBS News' Tony Guida reports that some experts are saying airport screeners can confiscate all the mascara and milk shakes they can find, but still another on-board threat lurks. Aviation consultant Michael Boyd says cargo is vulnerable to terrorists as well.
Boyd calls cargo "a wide-open place where people can inject things into airplanes."
And Rep. Edward Markey, D-Ma., who sits on the House Select Committee on Homeland Security, says more than 20 percent of all air cargo in the United States travels on passenger flights, Guida reports.
Chertoff reassured people things would only go so far.
Chertoff said the government was putting "less emphasis on the nail clippers and the nail scissors" and more on training additional screeners "specifically to look for modern-type detonation equipment that might be concealed in baggage."
TSA said it wanted to remove any ambiguity from its procedures, particularly over the handling of shoes.
Until now, the agency has strongly suggested removing shoes for the screening belt, but hasn't required that.
Now, travelers must take them off before walking onto airplanes. Flyers can continue to wear shoes containing gel heels, but they must remove any sort of gel sole insert and put those into checked baggage.
Airport travelers also should expect to see broader use of police-trained sniffing dogs, TSA said, along with random gate inspections and bag searches. But the TSA is limited by law to 45,000 screeners at the 450 commercial airports.
TSA chief Kip Hawley said the latest changes were based on feedback from security officers and the public.
"We are maintaining the same level of security while clarifying interpretations in the field," he said Sunday. "These tweaks are aimed at making a smoother process at the checkpoint."
The changes offer the same level of security that has been in place since last Thursday, but is intended to minimize the impact on travelers, officials said.
Screeners have begun searching more carryon luggage by hand. They also are randomly checking passengers at airport gates to make sure that they haven't bought toothpaste or drinks at airport shops after going through a security checkpoint.
Passengers are asked to arrive at least two hours early to allow for the additional screening. Those traveling to the United Kingdom should find out from their about any extra security measures or precautions that might be required. Laptop computers, mobile phones and iPods were among items banned on British flights.