The skin is one of the many miracles of the human body. It performs many essential tasks, such as protecting deeper tissues from damage, regulating body temperature, keeping water and bodily fluids inside the body, and keeping bacteria and other unwanted substances out of it. Another incredible property of our skin is its ability to vary in thickness over different parts of the body depending upon the function of that body part. For example, the skin on our back is subjected to more physical stress and exertion than our fingertips. Because of this, the skin on our back is thicker, giving the tissues underneath it greater protection from mechanical damage such as cuts and bruises. Meanwhile, the skin on our fingertips tends to be thinner, allowing them greater sensitivity to perform tasks requiring delicacy and agility. This greater sensitivity also helps protect our fingers from dangers our backs are not as likely to face, such as touching a hot stove.
The thinnest skin on the body is that covering the eyelids, which is around 0.5 mm thick. This is an important reason why the skin on and around the eyelids becomes wrinkled before the rest of the body. Skin contains a protein called elastin. This provides the skin's elasticity, allowing it to return to its original position when displaced. Elastin fibers are highly susceptible to UV rays, however. As we age, the Sun's rays destroy more and more of the elastin in our skin, causing it to toughen or become leathery as we age. Because the skin on our eyelids is so thin, it tends to lose its elasticity more quickly. This is one of the primary reasons why our eyelids generally develop wrinkles before the rest of the body.
The thickest skin of the body is on the palms of the hands and the soles of the feet. Both of these areas are about 4 mm thick, with the absolute thickest area of the skin being that covering the heels of the feet. These areas of the body are subjected to constant interaction with the external environment, and thus must be thick and callused. The skin covering our palms and soles is made even thicker by the stratum lucidum, a layer of the epidermis that is not present in any other part of the body. It should also be noted that these two areas of the body are hairless.
By understanding how the thickness of our skin is suited to our bodies, we can better understand how to care for our skin. For example, a burn affecting the thin, sensitive skin covering our eyelids could be far more dangerous than that same burn would be to the tough skin on our feet. The ability of our skin to adapt to the functions a body part must perform, as well as the dangers it face, is just another example of how truly amazing our bodies are.