The human skin is made up of several layers, and the outermost layer is called the epidermis, which sits directly on top of another layer called the dermis. Dermal papillae, sometimes called dermal pegs or DP, are small protrusions of the dermis layer into the epidermis layer. The DP serve several functions, including strengthening the adhesive bond between the dermis and epidermis, reducing the risk of separation between these two layers of skin, and providing blood flow to the epidermis, which has no blood supply of its own. Nerves coming through the dermis into the epidermis by way of the dermal papillae also serve the function of providing important sensory information, and these nerves are especially sensitive to pressure, pain, cold and heat. On the hands and feet, the pattern of the DP is visible in the form of fingerprints, also known as epidermal or papillary ridges.
Each individual protrusion of the dermis into the epidermis is called a dermal papilla. In its shape, a papilla looks similar to a finger or nipple, and the word is derived from the Latin word papula, meaning pimple. The part of the dermis where the dermal papillae are located is also called the papillary dermis or papillary layer. Approximately 20% of the dermis is made up of this papillary layer, which mainly consists of elastic connective tissue, blood vessels, touch receptors, and nerve endings.
Dermal papillae are an important part of skin anatomy. They contain the vascular loops and capillaries that transport oxygen and nutrients from the blood system to the epidermis, while simultaneously removing waste products from the epidermal layer. The epidermis mainly functions as a protective, exterior layer and has no nerve cells of its own, but the dermal papillae has specialized nerve endings that are extremely sensitive and provide vital sensory input from this outermost stratum of skin.
Dermal papillae are important in the formation of hair follicles, and are involved in the cycle of hair growth and shedding. A hair follicle is an indentation in the epidermis that sits right on top of a dermal papilla. In the case of a hair follicle, a dermal papilla is surrounded by what is called a hair matrix, which consists of epithelial cells, and pigment-producing cells that help form the hair itself as well as the root sheath the hair grows from. The access to the capillary blood vessel in a dermal papilla is vital for hair formation and growth.