How do shoes affect your feet?

They're made for walking, jogging, hiking, even dancing.

But in the centuries since our ancestors first wrapped their feet in woven grasses and animal skins to protect them from rough surfaces, function has clashed with fashion in the design of our shoes. The crocodile-hide loafers and cowboy boots that cross paths with dress oxfords on today's city streets are often chosen for what they say about their wearer rather than for comfort.

Among women's shoes, fashion has truly trumped function. As the summer months approach, colorful sandals, flip-flops, wedges, high heels and ballet flats dot the sidewalks. One of trendiest shoes this season is YSL's platform "Tribute" - with a tottering 5 1/2-inch heel. Often painstakingly selected to complete outfits, shoes like these put stress not just on feet, but on ankles, knees and backs, contributing to the approximately $3.5 billion spent annually in the United States for women's foot surgeries, which cause them to lose 15 million work days yearly.

Enduring discomfort to participate in fashion or show status is an age-old trend, said Elizabeth Semmelhack, a curator at Toronto's Bata Shoe Museum, which has about 13,000 footwear artifacts; the oldest is 4,500 years old, and the most recent was collected in 2006. "It's absolutely clear to me ... when I look at cultures that impracticality is one of the primary features among the privileged" class, she said.

Experts warn against what one group of foot doctors calls "cruel shoes" - such as the high heels that Semmelhack says have historically been "one of the primary ways to express what (people) don't have to do," such as walk long distances and do strenuous work.

Shoes with "pointed toes, shoes with thin soles, and shoes with high spike heels" are of the cruel variety, according to the Web site of the American Orthopaedic Foot & Ankle Society, because they can "cause crowding of the toes and increased pressure," which can result in hammertoes and bunions. The American Society of Podiatric Sports Medicine reports that a three-inch heel creates seven times more stress than a one-inch heel.

Years ago, lower classes did their best to mirror trends established by upper classes, Semmelhack said. For example, "in the 18th century, lower-class (women) might have heels, but (they) won't be as high" as those owned by upper-class women.

When humans walked barefoot, "societies seemingly had a low incidence of foot deformities and pain," according to a 1994 essay published in the Journal of the Southern Orthopaedic Association. The first shoes "were made in the shape of the foot and were sandals," wrote Sally A. Rudicel, an orthopedist at Tufts-New England Medical Center. But "over time ... as the shape of shoes changed, they became deforming forces on the foot and the source of pain."

Today, despite mounting evidence of the damage ill-fitting shoes can cause, women squeeze their toes to fit into oh-so-popular pointed-toe shoes, and they readily break the American Academy of Orthopaedic Surgeons' rule of thumb: no more than three hours in three-inch heels. Wearing heels causes your foot to slide forward, "redistributing your weight, creating unnatural pressure points and throwing your body's natural alignment out of whack," according to the Mayo Clinic. High heels have "been linked to overworked or injured leg muscles, osteoarthritis of the knee and low back pain," continues Mayo. "You also risk ankle injuries if you lose your balance and fall off your high heels."

For those women who want fashion plus function, so-called comfort-brand shoes claim to offer the best of both worlds. Among them: Naturalizer, Ecco, Aerosole, Cole Hahn and Taryn Rose, created by a former orthopedic surgeon who brought her first line of luxury shoes to the market in 1998. And they're not your grandmother's orthopedic shoes.

Foot doctors often recommend these lines to patients. "Comfort shoes tend to have a rounded toe box, more cushioning (and) more arch support," said Theresa Fahy, a podiatrist with offices in Virginia. The shoes make "you more comfortable when you're standing," she added.

Still, the lines aren't a cure-all for everyone, Fahy said. "It really depends on the foot. ... You don't really have a universal shoe for every foot."

But when it comes to properly fitting shoes, women often find a lack of options. "Men's shoes on the whole are available in a greater variety of widths and conform more closely to the outer dimensions of their feet," the foot and ankle society reports.

As a result, women are at greater risk for shoe-related health problems than men, according to the society, which released a recent position statement declaring that foot problems "resulting from poorly fitting shoes have reached epidemic proportions and pose a major health risk for women in America." Women account for about 90 percent of surgeries performed for the most common foot ailments, the society reports.

That risk can include bunions, stress fractures, joint pain in the ball of the foot, Morton's neuroma, "pump bumps" (enlargement of the bony area on the back of heel), corns and calluses, hammertoe, toenail problems and tight heel cords (shortening or tightening the Achilles tendon).

Women often think they're doing their feet a favor when they ditch the heels and put on flip-flops or ballet flats because there's no heel, no pointed toe, no reason to worry. Right?

Not so, say podiatrists, who treat foot problems often exacerbated by improper footwear. "The thing that flip-flops do best is carry patients into my office," said Stephen Pribut, a D.C. podiatrist. The repeated process of lifting your heel away from the shoe surface (creating that characteristic flip-flop sound) creates tension in the foot, said Pribut, which can worsen such painful inflammatory conditions as plantar fasciitis.

Erika Schwartz, a podiatrist in private practice in the Washington area, advised that ballet flats and flip-flops "really shouldn't be worn for any kind of excessive walking (because there's) really nothing giving you support underneath."

Nobody is advocating going barefoot on today's hard, trash-strewn surfaces; it's all about the right fit. "If your foot doesn't hurt during or within 24 hours after wearing a shoe," Pribut said, "go ahead and wear it. Otherwise, toss it and start over again."