Flip-flops have always been the summer footwear of choice to help cool the feet, not cause them to burn.

At least 10 people this summer, however, suffered burns and blisters along their feet from the airy shoes, which were purchased from several Wal-Mart stores across the U.S. The store has since stopped selling the flip-flops.

Dr. Nanette Silverberg, director of pediatric and adolescent dermatology at Beth Israel Medical Center in New York, said that the burning sensation is most likely due to allergies to the rubber on the shoes or to the chemical components, like Thiuram and Dithiocarbamates, used to break down the rubber in the shoes.

“When you think about the large distribution, it’s not likely that it’s the chemical coating that’s extremely toxic,” Silverberg said. “It can be allergic contact dermatitis, which is an allergy to something the skin comes in contact with. There are a variety of agents that can do it in flip-flops.”

In general, rubber allergies are a problem with most synthetic shoes, according to Silverberg. “When you have a contact allergy like that, it’s not usually latex but one of the ingredients used to process rubber,” she said. “Latex allergies are generally more severe, with hives, inhalational reaction where a blood test is conducted.

The first burn case was reported by a Florida woman on Aug. 31. She purchased the Sand-N-Sun flip-flops at Wal-Mart and later noticed a chemical burn along the area where the flip-flop bands touched her feet. The items were quickly removed from all store shelves nationwide following the other claims of foot burns due to the shoes, according to a Wal-Mart spokesman.

“When the first case of burning came to their attention with a customer in Florida, we found that there was more than one case,” said Wal-Mart's John Simley. “We asked stores to remove sandals from store shelves and prevented registers from selling them. The reason we’re doing that is because someone can pick them up and leave them in the sporting goods section, where someone else can pick them up and buy them. This is a way to assure that no one can purchase them.”

The company is also testing the Sand-N-Sun flip-flops and may continue to sell the line of shoes in the future once they find out more about the causes of the chemical burns. “Of the seven million sold, there were 10 cases of people having a reaction with them,” said Simley. “We have to know what we’re dealing with first. Clearly, seven million people were OK wearing them.”

In general, Silverberg said, flip-flops are usually not an issue because of the small area of skin being exposed to the shoe, and those who are allergic will notice a reaction within a couple of hours.

For flip-flop wearers who do have a chemical reaction to their shoes or any other synthetic shoe that is rubber based, Silverberg recommends that they visit a dermatologist to get a prescription for a topical cream like hydrocortisone and get a contact allergy test — a patch test where the doctor places pieces of allergens on a patient’s back to find their specific allergy.

She also recommends wearing shoes with white cotton socks while your feet are healing to absorb the sweat and apply some type of emollient to the feet.

“Not everyone in the population is that allergic,” added Silverberg. “That would account for why there are not thousands of cases. You don’t want to go out and buy another pair of flip-flops if you don’t know what’s really wrong.”