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.