List of skin conditions

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Young child with a red rash covering face, chest, shoulders, and arms
Rash due to measles

Many

arrector pili muscle.[4] In the embryo, the epidermis, hair, and glands form from the ectoderm, which is chemically influenced by the underlying mesoderm that forms the dermis and subcutaneous tissues.[5][6][7]

The epidermis is the most superficial layer of skin, a

stratum basale.[8] Nourishment is provided to these layers by diffusion from the dermis since the epidermis is without direct blood supply. The epidermis contains four cell types: keratinocytes, melanocytes, Langerhans cells, and Merkel cells. Of these, keratinocytes are the major component, constituting roughly 95 percent of the epidermis.[3] This stratified squamous epithelium is maintained by cell division within the stratum basale, in which differentiating cells slowly displace outwards through the stratum spinosum to the stratum corneum, where cells are continually shed from the surface.[3] In normal skin, the rate of production equals the rate of loss; about two weeks are needed for a cell to migrate from the basal cell layer to the top of the granular cell layer, and an additional two weeks to cross the stratum corneum.[9]

The dermis is the layer of skin between the epidermis and subcutaneous tissue, and comprises two sections, the

apocrine glands.[8] The dermis contains two vascular networks that run parallel to the skin surface—one superficial and one deep plexus—which are connected by vertical communicating vessels.[8][11] The function of blood vessels within the dermis is fourfold: to supply nutrition, to regulate temperature, to modulate inflammation, and to participate in wound healing.[12][13]

The subcutaneous tissue is a layer of fat between the dermis and underlying fascia.[14] This tissue may be further divided into two components, the actual fatty layer, or panniculus adiposus, and a deeper vestigial layer of muscle, the panniculus carnosus.[3] The main cellular component of this tissue is the adipocyte, or fat cell.[14] The structure of this tissue is composed of septal (i.e. linear strands) and lobular compartments, which differ in microscopic appearance.[8] Functionally, the subcutaneous fat insulates the body, absorbs trauma, and serves as a reserve energy source.[14]

Conditions of the human integumentary system constitute a broad spectrum of diseases, also known as

histologic information[22][23] that can be correlated with the clinical presentation and any laboratory data.[24][25][26]

Acneiform eruptions