Originally Posted by Wikipedia

High-heeled shoes cant the foot forward and down while bending the toes up. The more that the feet are forced into this unnatural position, the more it will cause the Achilles tendon to shorten. This will cause problems when the wearer chooses lower heels, flat-soled shoes, or to walk barefoot. When the foot cants forward, a disproportionately greater amount of the wearer's weight is transferred to the ball of the foot, increasing the likelihood of damage to the underlying soft tissue which supports the foot. In many shoes, style dictates function, either compressing the toes, or forcing them together, which results in blisters, corns, hammer-toes, bunions, and many other medical conditions, most of which are permanent, and will require surgery to alleviate the pain.

The best solution to avoid these problems is to avoid heels altogether. If that's not acceptable, then the wearer should ensure they're wearing high-heels no more than half the time, and that they're spending at least a third of the time on their feet either barefoot, in supportive flat-soled shoes, or in good running/walking/cross-training shoes. Saving high heels for rare occasions is best for the overall health of the feet.

One of the most critical problems with high-heels is with the design and construction of the toebox. Improper construction here wreaks the most damage and long-term pain on the foot. Narrow toe boxes force the toes together. Several celebrities, such as Victoria Beckham, have come to the point where surgery is needed to recover from the damage caused by wearing high-heels too often. Ensuring room exists for the toes to assume a normal position and spending sufficient time out of high-heels allows the body to repair any damage caused by high-heels, thereby recovering to a sufficiently healthy point where high-heel wear remains an option, rather than a debilitating practice. Unfortunately, the most common design trend today is towards the extremely pointed toe.

Block heels do not necessarily offer more stability, and any raised heel with too large a width, such as blade and block heels, induces unhealthy side-to-side torques to the ankle every step. Heels which strike the ground too far after of the ankle over-torque the ankle forward, producing extreme stress on the ankle, and creating additional impact on the ball of the foot, both of which are highly likely to cause damage to the feet. Thus, the best design for a high-heel is one with a narrower width, where the heel is closer to the front, more solidly under the ankle, where the toe box provides room enough for the toes, and where forward movement of the foot in the shoe is kept in check by material snug across the instep, rather than by toes jamming together in the toe box. Naturally, this rules out most pumps, but boots, particularly lace-ups with a round toe box and forward heel, are surprisingly supportive.

Interestingly enough, despite the medical issues surrounding high-heel wear, a few podiatrists recommend a well-constructed low heel of no more than two inches for their patients with flat feet. It appears the moderate heel improves the angle of contact between the metatarsals and the horizontal plane, thereby more closely approximating the angle and resulting weight distribution of a normally-arched foot. The angle for high-arched feet, however, is already exaggerated, and the wear of heels by those with high arches can be particularly problematic for the metatarsal phalangeal joint.

Regardless of fashions, it's important to note that high heels do cause cumulative damage to the feet. Many report back pain and problems with spinal alignment, from the abnormal posture that high heels induce.