While summer is in full swing, signs of back-to-school are everywhere, as retail stores fill their shelves with school supplies — most notably, backpacks.

"All of a sudden, we're in the midst of a summer heat wave, and the next thing you know, we're shopping ... and everything is back to school," says Teri Mitchell, of Safe Kids Upstate, a South Carolina organization.

Now is a good time for parents and children to brush up on backpack safety, Mitchell says. (In Hawai'i, the first day of school for most public school students will be July 30, July 31 or Aug. 1, the state Education Department said in a news release.)

"Parents need to buy a good, strong backpack that has good padding on the shoulders," she says. "Not to pack it too heavy, that's the big key."

A loaded backpack should equal no more than 15 percent of a child's body weight, Mitchell says.

But many people, regardless of age, tend to neglect their spinal health until they feel pain, says chiropractor Luke Henry, of Greenville, S.C. Research indicates that 80 percent of people will experience lower-back pain at some point in their lives.

"Clearly, heavy backpacks are part of the problem," he says.

Improperly used backpacks strain the neck, shoulders and back.

"I would say that it predisposes (children) ... to spinal health problems later in life," Henry says. "And when someone has back pain during adolescence, that greatly increases the likelihood of experiencing back pain throughout their life as an adult."

Backpacks that are too heavy or worn incorrectly also can result in poor posture, Henry says. "Chronic stress, poor posture and muscle imbalances can lead to pain and dysfunction."