The hands and the feet have much in common. They both have a different type of epithelium on the dorsal and plantar surface, they both have hair on the dorsal surface and none on the plantar surface, and they both have few sebaceous glands and numerous sweat glands on the plantar surface. However, there are many differences between the hands and the feet, the most important being that the feet constantly bear the weight of the body while the hands do not. The feet are used for locomotion, competitive athletics, and personal expression in the form of dance. They are forced into shoes that can function both as protection while walking and the source of bony deformity. One only need look at the bunions and overlapping toes of the woman who wore tall, spiked heel, pointed toe shoes during her youth who cannot walk normally today due to misshapen feet that cannot properly bear weight.
Anatomy of Physiology
The feet form our most important point of contact between the body and the earth. They grow proportionately as we grow during adolescence, pregnancy, and old age to provide the body with stable balance. Unfortunately, their bones wear out with continued use and chronic inflammation to yield crippling arthritis. The sole of the foot is made of keratin remarkably resistant to trauma from torque and pressure, but this resiliency is decreased when the keratin is wet. This most commonly occurs in individuals with sweaty feet. The interaction of sweat with the plantar keratin in the environment of the shoe creates unique hygiene challenges. The lack of oil glands on the sole of the foot also predisposes it to dry skin. This leads to our next topic of discussion, which is dermatologic disease of the feet.
Common Dermatologic Disease Considerations
As might be expected, the warm, moist, dark environment of the foot in the shoe is perfect for infection of all types, especially between the toes. The foot is a common site for bacterial, fungal, and yeast infections. These organisms can live on the surface of the foot or enter into the body through small wounds. Foot infection is a major medical issue in diabetics who have a reduced capacity to fight infection, poor blood circulation to the feet, and reduced sensation. In normal individuals, the most common infection of the feet is fungal, a condition known as tinea pedis. Tinea is the medical word for fungal infections of all types with pedis referring to the feet. Tinea pedis most commonly occurs between the toes, especially between the fourth and fifth toes, since these toes are usually closely spaced. Mild infections of this type can occur in otherwise healthy athletic individuals; however, the incidence of fungal infection increases with advancing age due to deterioration of the body’s immune system. Most fungal infections of the toes or the sole of the foot can be easily treated with two weeks of a topical antifungal. However, fungal infections of the nail require oral medication, usually for three months.
The foot is also the site of frequent viral infections in the form of plantar warts. The highly infectious human papilloma virus causes warts. This virus only affects humans, thus warts are passed by person-to-person contact through wounds in the foot. Common places to contract warts include public pools, exercise facilities, dance studios, public showers, etc., basically any place where there is moisture and lots of bare feet.
Other noninfectious growths that occur on the foot include calluses and corns. Calluses form over areas of the feet that are commonly traumatized, such as the side of the great toe, the side of the little toe, and the heel. Corns, on the other hand, occur over bony prominences. Hard corns occur on the sole of the foot at the base of the toes while soft corns occur over bones between the toes. Both calluses and corns are deposits of excess keratin designed to protect the foot from undue injury while walking. Unfortunately, the calluses and corns themselves may produce pain while walking. Substances can be applied to the growths to remove the keratin, but the callus or corn will return unless the exact cause for their formation has been determined. This can be ill-fitting shoes, arthritic changes, or improper weight transfer over the foot while walking.
The foot is also a common site for eczema or dry skin due to the complete lack of oil glands on the sole and the reduced number of oil glands on the top of the foot. The feet receive the most cleanser and water contact of any part of the body while showering, thus excessive removal of sebum on the feet is common. For all of the reasons put forth here, the feet have unique hygiene needs to balance the predilection for infection with the dryness of overcleansing.
Hygiene Needs
The feet need aggressive hygiene, not only to prevent infection, but also to control odor. Foot odor is primarily due to the mixture of sweat with bacteria in the closed environment of the shoe. Bacteria digest the sweat to obtain nutrition and reproduce. Most individuals have several types of bacteria present in low numbers on the feet. The difference between individuals with minimal foot odor and extreme foot malodor is the number and type of bacteria present on the feet. Foot malodor is a much greater problem in persons with hyperhidrosis. Hyperhidrosis of the feet is identical in cause to hyperhidrosis of the palms, in that both are primarily under emotional control, although feet tend to sweat more for thermoregulatory purposes due to the presence of warm socks and shoes.
Good cleansing of the feet is a prerequisite to skin health, but overly aggressive cleansing may set the stage for dry skin and foot eczema. Thus, foot cleansing must be carefully balanced with proper moisturization, our next topic of discussion.
Skin Care Needs
One way to minimize the dryness that may be associated with foot cleansing is through the use of moisturizers. Moisturizers can be used to prevent foot dryness and soften calluses utilizing substances such as urea and lactic acid to open up water binding sites on dehydrated keratin. The physical act of rubbing a moisturizer on the feet can also help desquamate dead skin that may build up between the toes and on the arch of the foot, especially in elderly individuals. Foot moisturizers must be similar to hand moisturizers in that both occlusive and humectant substances must be incorporated.