How to tell it's time to throw out your shoes

Dearly beloved, we are gathered here today to bid a fond farewell to some cherished companions: our shoes.

From the faithful running shoe to the whimsical sandal, from the sensible work loafer to the sexy stiletto, all shoes reach a point at which they have outlived their usefulness, and we must let them go.

Our time together may seem fleeting, but we hang onto favorites past their prime at our peril.

"The shoe wears out in the area where we overload it, so the part where you need the most support isn't there," said Minneapolis podiatrist Paul Langer, clinical professor at the University of Minnesota. "A worn shoe can exaggerate the biomechanical faults you already have."

A loss of support and cushioning can cause shin splints, Achilles tendinitis, knee pain and plantar fasciitis, a common form of heel pain. As a shoe's sole and heel wear down unevenly, the likelihood of twisting an ankle increases. In severe cases, old shoes can cause stress fractures, Langer said.

Unfortunately, there's no clear expiration date for a shoe, whose life span depends on the quality of construction, how well you take care of it and where and how often you wear it. But there are some guidelines for determining when it's time for your shoes to pass on. The following guide to shoe death draws from the advice of Langer, author of "Great Feet for Life: Footcare and Footwear for Healthy Aging" (Fairview; $14.95)"; Karen Langone, president of the American Academy of Podiatric Sports Medicine; and cobbler Randy Lipson, owner of Cobblestone Shoe Repair in St. Louis.

ATHLETIC SHOES

The cushioning on these wears down fastest because they suffer from fast starts, stops and changes in direction, plus more pressure than walking shoes, Langer said. When you run, the pressure you put on the shoe is two or three times your body weight. When you land from jumps in sports such as basketball or volleyball, the pressure is 7 to 8 times your body weight.

As a general rule, the life of a running shoe is 300 to 500 miles, Langer said, though it varies with your body weight, gait and surface on which you run. Following that rule, someone who runs 4 miles, four times a week should consider replacing shoes after about 6 months, while a more casual athlete could wait a year. Running shoes typically can't be repaired.

One way to check if running shoes need to be replaced is to look at the midsole, which is the foam part of the shoe between the outer sole (the bottom of the shoe, where the treads are) and the upper (the top of the shoe, where the laces are). When it starts to wrinkle deeply, the shoe is losing its cushioning and getting worn out. The midsole warps with heat, sun exposure and moisture, so if you run somewhere damp, it breaks down faster.

CASUAL WORK OR WALKING SHOES

As a rule of thumb, Langone said, if you wear a pair of shoes to work three to four times a week, after a year or so they'll either need fixing or trashing. You know it's time to repair or replace when you have scuffed heels or flat spots on the outer sole, or when the back edge of the heel gets so worn that it's angling sharply, Langone said. Another sign is when inside pieces of the shoe poke through, like a nails showing in the heel. One test is to set the shoes on a flat surface and look at them from behind, Langone said. If they tilt to the side, it's time to fix or toss.

LEATHER DRESS SHOES

If you buy good-quality shoes and take good care of them, resoling and re-heeling when necessary, they could last five to 15 years, Lipson said. Whether repairing is worth the cost depends on how much you paid for the shoes in the first place, as high-quality leather resoling runs $35 to $45. If they're inexpensive shoes, it's probably smarter to just buy new ones. (The leather sole needs replacing if when you put your thumb in the center of the outer sole at the ball of the foot, the leather feels soft instead of firm.) A component to keep an eye on is the leather on the upper part of the shoe, which can get stiff if not regularly cleaned, polished and conditioned, Lipson said. Once it hardens, the leather can crack where the shoe bends, and there's nothing you can do about that. In addition, these shoes can suffer damage to the toe box, the cardboard frame at the toe of the shoe, such as indentations from kicking or being stepped on. That's too costly to fix, Lipson said, so it's time to toss.

HIGH HEELS

Because the heels are narrower and the soles are usually thinner, high heels wear down faster than flatter shoes, Lipson said. The most wear happens near the toe on the bottom of the shoe, because that's the area that bears the most weight. If the thickness of the sole has worn down by half, it's time to resole or replace.

The heel also wears down quickly, so as soon as you start to see the nail poke through, get new heel lifts. High-quality heel lifts can last twice as long as the originals from the manufacturer, Lipson said.

SANDALS, FLIP-FLOPS

The upper part of a sandal bears a lot of stress to keep the foot in place, making for a shorter life than enclosed shoes, Langone said. Stretched or broken straps mean it's time to replace or, if they're very expensive shoes, repair.

The same heel and sole issues apply to sandals as other shoes. So if those Crocs are starting to look like lopsided pancakes, time for a new pair.

TREAD LIGHTLY

To minimize the eco-impact of tossing your footwear, consider these options:

For gently worn shoes, donate them to a charity such as Soles4Souls, which distributes them to the needy.

For athletic shoes that no longer have any business being on anyone's feet, submit them to Nike's Reuse-A-Shoe program. The company separates the shoe's materials — the rubber from the foam from the fabric — and grinds them down to make raw materials for running tracks, tennis and basketball courts. Visit nikereuseashoe.com for drop-off spots.