The dermis, which lies just beneath the epidermis, is 1.5 to 4 millimeters thickthe thickest of the three layers of the skin. It’s also home to most of the skin’s structures, including sweat and oil glands (which secrete substances through openings in the skin called pores, or comedos), hair follicles, nerve endings, and blood and lymph vessels. But the main components of the dermis are collagen and elastin.
Collagen is a tough, insoluble protein found throughout the body in the connective tissues that hold muscles and organs in place. In the skin, collagen supports the epidermis, lending it its durability. Elastin, a similar protein, keeps the skin flexible. This is the substance that allows the skin to spring back into place when stretched: the scientific reason a funny face won’t stay that way, no matter what your mother told you. The properties of collagen and elastin fade with age, giving rise to wrinkles and sagging skin.
In addition to collagen and elastin, you’ll find water in the dermis. In fact, much of the body’s water supply is stored there. When the amount of stored water is increasedfor example, when you’re retaining waterthe skin becomes tight and stretched as it expands to accommodate the surplus. The dermis also contains scavenger cells from the immune system. In the event that a foreign organism makes it past the epidermis, these cells will engulf and destroy it.
Several structures can be found in the dermis. Sweat glands, numbering about 3 million in the average person, are the most numerous and are classified according to two types: the apocrine glands and the eccrine glands.
Apocrine glands are specialized sweat glands that can be found only in the armpits and pubic region. In animals, it is the apocrine glands that secrete the scents used to attract a mate; however, no one is sure of their function in humans. What we do know is that these glands secrete a milky sweat that encourages the growth of bacteria responsible for body odor. These glands are activated at puberty when stimulated by hormones.
The eccrine glands are the true sweat glands. Found over the entire body, these glands regulate body temperature by bringing water via the pores to the surface of the skin, where it evaporates and releases heat. These glands respond to heat, exercise, and fever, and some eccrine glands, such as those on the palms, respond to emotional stress, as well. It’s these glands that give you clammy hands when you’re nervous.
Unlike apocrine glands, eccrine glands function from childhood, though they do increase their activity at puberty. Though these glands can produce up to two liters of sweat an hour when they’re working at their full potential, they’re not usually to blame for body odor. These glands secrete mostly water, which doesn’t encourage the growth of odor-producing bacteria.
The dermis is also home to the sebaceous, or oil, glands, which are attached to hair follicles, cylindrical structures that house the roots of the hair. Sebaceous glands can be found everywhere on the body except for the palms of the hands and the soles of the feet. Usually called into action by hormones during puberty, these glands secrete oil that helps keep the skin smooth and supple. The oil also helps keep skin waterproof and protects against an overgrowth of bacteria and fungi on the skin. At times, these glands overproduce and cause acne, a condition in which pores become clogged and inflamed.
Nerve endings can also be found in the dermis. Of course, these structures are responsible for the sense of touch, relaying information to the brain for interpretation. They also signal temperature to the brain and, if necessary, trigger shivering, an involuntary contraction and relaxation of muscles. This muscle activity generates body heat.
Finally, blood and lymph vessels are found in the dermis. The blood vessels bring nutrients and oxygen to the skin and remove cell waste and cell products. The blood vessels also carry the vitamin D produced in the skin back to the rest of the body. Enlarged vessels that can be seen through the skin are known as spider veins or varicose veins. Broken blood vessels appear as bruises.
The lymph vessels bathe the tissues of the skin with lymph, a milky substance that contains infection-fighting immune system cells. The cells work to destroy any infection or invading organisms as the lymph gradually circulates back through the body’s tissues to the lymph nodes.
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