According to Kelley Styring, author of In Your Purse: Archaeology of the American Handbag, the average American woman packs 67 items in her purse. The extra weight of all this stuff, doctors warn, can lead to a plethora of painful problems.

Studies about the effects of carrying heavy bags and backpacks, conducted by Kevin Slates, a researcher and occupational and environmental health expert at Indiana University, show that lugging around a load of improperly distributed books or materials day after day can cause compressed nerves, uneven stress on the spinal column, strain on the knee or hip and bouts of acute or chronic pain.

The solution, notes Slates, is that handbags shouldn’t weigh more than 10 to 15 percent of our body weight. And stay balanced: Carry a bag on one shoulder and a tote in the other hand.