The biology of the skin of the feet

Like the hands, the feet are extensions of the body that have very specific, important functions. The skin that covers the feet is equally as specially designed and is divided into two sections: the dorsal skin and the plantar skin, each with different functions and innervation. The boundary between one and the other can be easily spotted when it comes to certain skin conditions that affect only one of the two areas, for example in cases of psoriasis or plantar hyperkeratosis.

The figures below show cases of psoriasis. However, the condition affects only the dorsal region of the foot and spares the plantar in Figure 1; while in Figure 2, the condition affects the plantar and not the dorsal skin.

As shown in both Figures 1 and 2, the plantar region includes the edges of the foot, which is further evidence of a clear demarcation between the two areas of the skin.

Cutaneous areas of the foot

The dorsal skin on the foot is similar to that of the skin on the legs. It has a thin stratum corneum, scattered hair follicles and a few eccrine sweat and sebaceous glands.
Instead, the plantar area and sides of the foot area are quite different. This skin has a thick stratum corneum, no hair, many eccrine sweat glands and no sebaceous glands.
In terms of tactile-thermal nerve endings, those in the plantar area are far more developed than those in the dorsal.

The anatomy of the dorsal and plantar regions

The dorsal skin is softer to the touch than that of the plantar area. It is more fragile, and reddens more easily.
On the other hand, the more robust plantar area is rough, dry to the touch and is unlikely to redden.
These differences are further highlighted when the areas are affected by skin conditions. For example, the dorsal area can often show allergic reactions after contact with certain footwear and is where eczema can develop. On the other hand, eczema is almost unheard of in the plantar region. At the same time, mycoses from dermatophytes can spread to the plantar region, but very rarely affect the dorsal.

Treatment for conditions will also depend on the area of the foot they have affected. For example, keratolytic cream, which can be used to reduce the thickness of the stratum corneum in cases of plantar hyperkeratosis, must only be used on the plantar region and on the sides of the foot. If used on the dorsum, it would cause considerable irritation as the stratum corneum of the area is already fragile.