If you're packing lunch for your kid, chances are it will end up at unsafe temperatures before it's eaten.

That's according to a Texas study that tested more than 700 preschoolers' lunch packs and found less than two percent of the meats, vegetables and dairy products were in the safe temperature zone.

"It was a shock when we discovered that more than 90 percent of the perishable items in these packed lunches were kept at unsafe temperatures," said Fawaz Almansour, a doctoral student at the University of Texas in Austin.

His study, released on Monday in the journal Pediatrics, is the first to check how the food that kids' bring to school is doing about an hour and a half before lunchtime.

According to the U.S. Centers for Disease Control and Prevention, perishable foods kept between 40 degrees and 140 degrees Fahrenheit (4 to 60 degrees Celsius) for more than two hours are no longer safe to eat.

Although 45 percent of the packed lunches included an ice pack and 12 percent were kept in refrigerators, nearly all of the perishable foods were in the danger zone.

That means bacteria that cause food poisoning -- like E. coli and Salmonella -- could be multiplying quickly inside the sandwiches that kids eat, Almansour said.

According to the CDC, one in six Americans gets food poisoning every year, but it is unclear how many cases are caused by lukewarm sack lunches.

"This study is an eye-opener more than anything else," Almansour told Reuters Health. "It shows there is a problem."

His recommendation? Pack the lunch with lots of icepacks, and have your kid take it out of the container at school and put it in the fridge.

SOURCE: bit.ly/cxXOG Pediatrics, online August 8, 2011.