Anatomy Skin

From acne to xerosis, skin conditions number in the hundreds. In fact, some doctors, called dermatologists, specialize in disorders of the skin, but is it any wonder: the skin is the largest organ in the body. The skin of the average adult male covers more than two square yards and weighs about ten pounds.

Not “Only Skin Deep”

The skin is more than what you see on the surface. It’s actually made up of three distinct layers, each serving a special function, and ranges from 0.5 mm in the eyelid to 2 mm in the palm of the hand. (1 inch is about 25 millimeters.)

The top layer is the epidermis and is in itself composed of several layers. The “living layer” is what produces the cells that make up the epidermis. As the cells age they are pushed to the surface to form the “dead” layer, which acts as a first line of defense against toxins, foreign bodies, and sun. These dead cells are then sloughed off to make room for other dead cells. The whole process takes about four weeks.

The middle layer is the dermis. Often called the “true skin,” the dermis contains, like other organs, muscle cells, nerve fibers, and blood vessels called capillaries. What makes it unique, however, is the presence of sweat and sebaceous glands and hair follicles. Sebaceous glands produce an oily substance, called sebum, which lubricates and protects the skin. Sweat glands are part of the body’s cooling system; as sweat evaporates, body temperature drops. Capillaries are also integral to cooling: when body temperature rises, blood vessels dilate causing the flush seen with fever or overexertion.

The deepest layer is the subcutaneous layer. This layer specializes in fat production, and is also key to the manufacture of vitamin D.

Skin Anatomy

Skin Term Definitions

The following are some terms that apply to skin, skin irritations and skin disorders.

Acne: A localized inflammation caused by hyperactivity of the oil glands at the base of hair follicles combined with blockage of the outflow tract due to excess keratin production.

Alopecia: Hair loss. Alopecia can be localized to one or more areas of the scalp (alopecia areata), or can result in total loss of scalp hair (alopecia totalis) or hair loss over the entire body (alopecia universalis).

Birthmark: A visible mark due a localized area of pigmentation or collection of blood vessels.

Blister: A pocket of fluid under the epidermis. A blood blister is filled with blood and is due to injury. A fever blister, or cold sore, is caused by herpes simplex virus 1 (HSV1). A water blister is filled with clear serum.

Boil: A skin abscess; a tender, red, swollen area filled with pus. Boils can be caused by bacteria, clogged sebaceous glands, or inflammation of the sweat glands.

Callus: A localized thickening of the epidermis due to regular friction.

Carbuncle: A skin abscess typically not responsive to antibiotics. Hot pack application and draining of pus accumulation is the usual treatment. Carbuncles can be indicative of a more serious condition if accompanied by fever or long-term illness.

Comedones: Plural of comedo, a hair follicle filled with dead skin cells, sebum and bacteria. Closed comedones are known as whiteheads. Open comedones are called blackheads. Comedones are the primary sign of acne.

Corn: A small callus caused by regular irritation to the skin over a bony projection. Corns often occur over a toe (hard corn) or between the toes (soft corn).

Crust: A scab.

Cyst: A closed capsule filled with fluid or thick material. A sebaceous cyst occurs deep in the skin and is filled with sebum that is grayish, cheesy and foul smelling. Sebaceous cysts are common on the face, neck, and trunk. Generally painless, sebaceous cysts can become inflamed and tender, at which point they can be surgically drained. Recurrence of a drained sebaceous cyst is not uncommon.

Dermatitis: Inflammation of the skin. Often, the terms “dermatitis ” and “eczema ” are used synonymously.

Eczema: A group of skin disorders characterized by inflammation, which can cause tiny blister-like bumps that turn red and form a crust. Eczema, in all its forms, is typically itchy and may cause a burning sensation.

Folliculitis: An inflammation of the hair follicles generally caused by the hair folding back on itself. It occurs most often in areas that are shaved. In men folliculitis commonly occurs on the cheeks and neck; in women folliculitis is most common in the bikini area.

Freckles: Tan or brown spots that most often occur in light complected people (especially those with red hair). Freckles appear after repeated exposure to the sun. Although not dangerous in themselves, freckles are a warning that the skin is vulnerable to sunburn and skin cancer.

Hives: A raised, itchy area usually caused by an allergic reaction. Hives may last for days or weeks, but usually only for a few hours. Hives are also called urticaria.

Hyperpigmentation: Dark spots on the skin. Although typically cosmetic, some cases of hyperpigmentation are a sign of an underlying medical condition.

Impetigo: A spreading, patch of red, itchy skin that forms pustules which become crusty, mustard yellow sores. Impetigo is a bacterial infection typically caused by Staphylococcus (staph) or Streptococcus (strep) that requires antibiotic treatment. Impetigo is most common in children, and generally occurs on the face or arms, although it can occur on other parts of the body, as well.

Keloid: An overgrown scar that rises above the surface of the skin.

Keratin: A fibrous protein that adds tensile strength to the skin. Also found in hair and nails.

Lesion: A sore.

Macule: A flat blemish.

Melasma: An area of pigmentation on the cheeks affecting about half of pregnant women. Also called the “mask of pregnancy. “

Milia: Whiteheads.

Mole: A raised, pigmented spot.

Nodule: A small solid bump that can be felt in the skin. Nodules can occur in any layer of the skin. Nodules range from 1 to 2 cm in diameter. (1 inch = 2.5 centimeters.)

Papule: A pimple. A small solid bump that rises above the surface of the skin. Papules are generally smaller than 1 cm in diameter. They can become infected and crusty when broken.

Psoriasis: A red, scaly skin irritation that typically affects the skin of the elbows, knees or scalp, and the skin in or around the ears, navel, genitals or buttocks. Some cases are thought to be an autoimmune response. About ten to fifteen percent of patients with psoriasis will also develop arthritis (psoriatic arthritis).

Pustule: A little pimple filled with pus in the epidermis or dermis. Pustules typically occur in sweat glands or hair follicles.

Rash: A red, itchy skin irritation.

Rosacea: A chronic reddening of the forehead, nose, cheeks and chin caused by enlarged capillaries. Pimples may also occur. Rosacea is often confused with adult acne.

Scar: A mark caused by healing tissue.

Ulcer: A sore that, due to erosion, is below the level of the surrounding tissue.

Urticaria: A raised, itchy area usually caused by an allergic reaction. Urticaria may last for days or weeks, but usually only for a few hours. Urticaria are also called hives.

Vesicle: A small blister.

Vitiligo: Loss of pigmentation. Thought to be an autoimmune response, vitiligo results in white patches of skin anywhere on the body. The hair in affected areas may also turn white. Vitiligo affects one to two percent of the population.

Xerosis: Dry skin.

Resources

American Academy of Dermatology. (1999). Acne. Retrieved March 19, 2002, from www.dermatologychannel.net/follicle/acne/.

American Academy of Dermatology. (1999). Patient information pamphlets. Retrieved March 19, 2002, from www.aad.org/pamphlets/.

National Library of Medicine. (updated 2001). Sebaceous cyst. Retrieved March 20, 2002, from www.nlm.nih.gov/medlineplus/ency/article/000842.htm.

National Skin Centre (Singapore). (nd). Information on common skin diseases. Retrieved March 19, 2002, from www.nsc.gov.sg/cgi-bin/WB_GroupGen.pl?id=33.