Acne is the term for plugged pores (blackheads and whiteheads), pimples, and even deeper lumps (cysts or nodules) that occur on the face, neck, chest, back, shoulders and even the upper arms. Acne affects most teenagers to some extent. However, the disease is not restricted to any age group; adults in their 20s – even into their 40s – can get acne. When severe, acne can lead to serious and permanent scarring. Even less severe cases can lead to scarring and psychological trauma. Perioral dermatitis is an acneiform eruption that occurs in women over the age of 30. Rosacea is an acne like eruption of the face that occurs in people over the age of 30. Hidradenitis is a disease that resembles cystic acne but occurs in the axilla and groin.
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Conditions of the human integumentary system constitute a broad spectrum of diseases, also known as dermatoses , as well as many nonpathologic states (like, in certain circumstances, melanonychia and racquet nails ).   While only a small number of skin diseases account for most visits to the physician , thousands of skin conditions have been described.  Classification of these conditions often presents many nosological challenges, since underlying etiologies and pathogenetics are often not known.   Therefore, most current textbooks present a classification based on location (for example, conditions of the mucous membrane ), morphology ( chronic blistering conditions ), etiology ( skin conditions resulting from physical factors ), and so on.   Clinically, the diagnosis of any particular skin condition is made by gathering pertinent information regarding the presenting skin lesion (s), including the location (such as arms, head, legs), symptoms ( pruritus , pain), duration (acute or chronic), arrangement (solitary, generalized, annular, linear), morphology ( macules , papules , vesicles ), and color (red, blue, brown, black, white, yellow).  Diagnosis of many conditions often also requires a skin biopsy which yields histologic information   that can be correlated with the clinical presentation and any laboratory data.