Many conditions affect the human integumentary system—the organ system covering the entire surface of the body and composed of skin, hair, nails, and related muscle and glands. The major function of this system is as a barrier against the external environment. The skin weighs an average of four kilograms, covers an area of two square metres, and is made of three distinct layers: the epidermis, dermis, and subcutaneous tissue. The two main types of human skin are: glabrous skin, the hairless skin on the palms and soles (also referred to as the "palmoplantar" surfaces), and hair-bearing skin. Within the latter type, the hairs occur in structures called pilosebaceous units, each with hair follicle, sebaceous gland, and associated arrector pili muscle. 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.The epidermis is the most superficial layer of skin, a squamous epithelium with several strata: the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale. 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. 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.
Impetigo herpetiformis
Intrahepatic cholestasis of pregnancy (cholestasis of pregnancy, jaundice of pregnancy, obstetric cholestasis, prurigo gravidarum)
Linea nigra
Pemphigoid gestationis (gestational pemphigoid, herpes gestationis)
Prurigo gestationis (Besnier prurigo, early-onset prurigo of pregnancy, linear IgM dermatosis of pregnancy, papular dermatitis of pregnancy, prurigo of pregnancy, Spanglers papular dermatitis of pregnancy)
Pruritic folliculitis of pregnancy
Pruritic urticarial papules and plaques of pregnancy (late-onset prurigo of pregnancy, polymorphic eruption of pregnancy, PUPPP syndrome, toxemic rash of pregnancy, toxic erythema of pregnancy)
Striae gravidarum

Pruritic
Pruritus, commonly known as itchiness, is a sensation exclusive to the skin, and characteristic of many skin conditions. Adult blaschkitis
Aquadynia
Aquagenic pruritus
Biliary pruritus
Cholestatic pruritus
Drug-induced pruritus
Hydroxyethyl starch-induced pruritus
Lichen simplex chronicus (neurodermatitis) 
Prion pruritus
Prurigo nodularis
Prurigo pigmentosa
Prurigo simplex
Pruritus ani
Pruritus scroti
Pruritus vulvae
Puncta pruritica (itchy points)
Scalp pruritus
Senile pruritus
Uremic pruritus (renal pruritus)

Psoriasis
Psoriasis is a common, chronic, and recurrent inflammatory disease of the skin characterized by circumscribed, erythematous, dry, scaling plaques. Annular pustular psoriasis
Drug-induced psoriasis
Exanthematic pustular psoriasis
Generalized pustular psoriasis (pustular psoriasis of von Zumbusch)
Guttate psoriasis (eruptive psoriasis)
Inverse psoriasis
Keratoderma blennorrhagica (keratoderma blennorrhagicum)
Localized pustular psoriasis
Napkin psoriasis
Psoriasis vulgaris (chronic stationary psoriasis, plaque-like psoriasis)
Psoriatic arthritis
Psoriatic erythroderma (erythrodermic psoriasis)
Seborrheic-like psoriasis (sebopsoriasis, seborrhiasis)

Reactive neutrophilic
Reactive neutrophilic cutaneous conditions constitute a spectrum of disease mediated by neutrophils, and typically associated with underlying diseases, such as inflammatory bowel disease and hematologic malignancy.