Glossary

Abscess
An infection that leads to a collection of pus within the tissue.

Ablation
Removal, such as by an ablative laser.

Acne
Acne is a common skin problem that shows up as outbreaks of bumps, papules and/or pustules often called pimples or zits. Acne lesions usually appear on the face, neck, back, chest, and shoulders. Although most people associate the disorder with teenagers, acne can emerge at any age until menopause, especially during times of hormonal flux.

Acne occurs when excess sebum created by the sebaceous glands, builds up beneath the skin within a hair follicle (“pore”). This creates a small bump called a “comedo”. A comedo may be referred to as a “blackhead” if the sebum has darkened upon exposure to air. The sebum can become infected with bacteria (p. acnes) which causes the lesion to become red and inflamed. The severity of acne is determined by the extent of the lesions and the degree of inflammation.

Acute
A condition that has appeared recently or is of a short duration. The opposite of chronic or long-lasting.

Aldara (imiquimod)
A prescription medication applied to the skin that is FDA approved for the treatment of actinic keratoses (AKs), superficial basal cell carcinoma (BCC), and external genital warts (EGW). It works by activating the body's own immune system. When Aldara is applied to the skin, immune cells are activated and travel to the area.

Allergen
A substance that triggers an allergic reaction in people who are sensitive to it.

Alopecia
Hair loss.

Alopecia, androgenic
Hair loss in men and women from hormonal changes to the hair follicles. In men, it is referred to as “male pattern baldness."

Alopecia areata
Alopecia areata is an autoimmune and often reversible disease in which hair loss occurs in sharply defined patches, usually involving the scalp or beard. In most cases of alopecia areata, hair falls out in small, round patches about the size of a quarter. In many cases, the disease does not extend beyond a few bare patches. However, in some people, the hair loss is more extensive.

Alopecia totalis
A form of alopecia areata that leads to total hair loss from the scalp and face.

Alopecia universalis
A form of alopecia areata that leads to total hair loss on the scalp, face, and body.

Anagen
The growing phase of the hair follicle. Each hair follicle goes through a growth phase (anagen) that last several years, before a resting phase (telogen) that last several months. Finally there is the declining phase (catagen).

Atopic Dermatitis
Atopic dermatitis, sometimes referred to as “ eczema ” is a chronic skin disorder that causes dry, itchy, and inflamed skin. The rash of Atopic dermatitis comes and goes in cycles. The worsening of atopic dermatitis (“flares”) can be brought on by a variety of triggers.

Atopy (atopic)
A genetic predisposition to the development of hypersensitivities, including allergies, and asthma.

Atrophy
A decrease in the volume of tissue. Atrophic skin is thin and may appear slightly sunken.

Autoimmune disease
A disease that occurs when the immune system mistakenly attacks the body's own tissues ("auto" means self). Examples include rheumatoid arthritis and systemic lupus erythematosus.

Basal cell
A type of skin cell found in the lowest levels of the epidermis. These generate new skin cells (keratinocytes) that grow to the surface of the skin.

Biopsy (skin)
The removal of tissue to diagnose a skin disorder.

Blackhead comedo

Blister
An enclosed collection (bubble) of fluid within or beneath the epidermis.

Blue nevus
A benign mole with a dark blue color that results from the pigment being in the deep layers of the skin. Seen most often in older children or adolescents.

Bulla
Large blister that measures at least 1cm (0.4 inches) at its widest point. Larger than a vesicle.

Bullae
Plural of bulla.

Catagen
The declining phase of the hair follicle. During catagen, the hair follicle shrinks. Each hair follicle goes through a growth phase (anagen) that last several years, before a resting phase (telogen) that last several months. Finally there is the declining phase (catagen). 

Cellulitis
An infection of the skin, usually by bacteria (staph and strep).

Chronic
Long-lasting. The opposite of acute.

Collagen
A protein in the dermis layer of skin that provide skin with its bulk and strength. A reduction in collagen, as occurs with aging, causes skin to lose its fullness.

Comedo
A dilated hair follicle and sebaceous gland filled with sebum and bacteria. A comedo may be "open" in which the sebum is exposed to the air causing the sebum inside to turn dark or black. This is referred to as a “blackhead.” A comedo may be “closed” in which the sebum inside remains white. This is referred to as a “whitehead.”

Comedones
Plural of comedo.

Corticosteroids
A family of medications used to control inflammation. Different from the “steroids” (anabolic steroids) used by athletes and body builders. May be taken by mouth (prednisone) or applied topically to the skin (1% hydrocortisone cream).

Topical corticosteroids may be ranked on their strength. Group 1 (I) corticosteroids are "super potent" and have the greatest risk of side effects if used for prolonged periods. Group 7 (VII) corticosteroids are “low potency” and include 1% hydrocortisone that can be purchased over the counter.

Cryotherapy
A cold substance, such as liquid nitrogen, is used to remove skin lesions.

Dermal filler
A substance injected into the dermis to give the skin a fuller look.

Dermatitis
A general term used to describe inflamed skin. There can be many causes of dermatitis, such as an allergic reaction or atopic dermatitis. Dermatitis can be short-term ("acute") or long-term ("chronic"). Acute dermatitis causes the skin to appear red, blistered or swollen. Chronic dermatitis causes the skin to appear thickened, rough, and darker than the surrounding skin.

Dermatology
The medical specialty focused on the diagnosis and treatment of people with skin conditions (including hair and nails).

Dermatologic surgery
The diagnosis, treatment and repair of clinical and cosmetic problems of skin, hair, nails, and other tissues by surgical and non-surgical methods. Procedures include laser surgery, cryosurgery, excision, Mohs surgery, dermal fillers, and hair restoration. Also called dermasurgery.

Dermatophyte
A fungi that lives on the top layer of the skin. Found on all people, including those with normal skin. May overgrow, leading to problems such as athlete’s foot (tinea pedis) or tinea versicolor.

Dermis
The deep layer of skin that lies below the epidermis. Contains collagen, blood vessels, nerves, sweat glands (eccrine glands), and sebaceous glands.

Ecchymoses
Bruises

Elastin
A protein found in the dermis layer of skin that provides skin with its elasticity. The loss of elastin, as occurs with aging, leads to skin that loses its shape.

Electrodessication and curettage (ED&C)
The removal of skin growth with a rounded knife (curette). The wound is heated to prevent bleeding. May be used to treat certain types of skin cancer or precancerous lesions. A local anesthetic is injected before the procedure.

Epidermis
The top layer of skin that lies above the dermis. It is composed primarily of a type of squamous cell called a keratinocyte. Cells at the base of the epidermis (basal cells) generate keratinocytes that grow to the surface. The epidermis replaces itself every 12-14 days. There are no blood vessels in the epidermis so a cut or scrap of the epidermis does not bleed

Erysipelas
A type of cellulitis.

Erythema
Redness of the skin that is greater than the surrounding skin. May be a sign of inflammation from flushing, infection, sunburn, or other conditions.

Exanthem
An acute rash that results from an infection, particularly viruses.

Excision
The removal of a skin growth with a scalpel. The wound is usually closed with stitches. If done for purposes of a biopsy, the tissue may be sent to a laboratory for further examination under a microscope.

Exfoliation
The removal of the top layer of skin. This may occur naturally as the result of a skin disease, such as sunburn. Or it may result from an elective procedure such as dermabrasion or microdermabrasion.

Fitzpatrick type
A scale used to measure the darkness of skin. Fitzpatrick type I describes someone who is pale, with very little skin pigment, who easily sunburns. Fitzpatrick type IV describes someone who is dark with a lot of skin pigment who easily tans when exposed to sunlight.

Folliculitis
The inflammation of one or more hair follicles, usually due to a bacterial infection.

Furunculosis
Also known as boils, acute collections of pus, or abscesses arising from several hair follicles and surrounding tissue.

Hair bulb
A bulbous collection of actively growing cells at the base of a hair follicle that constantly produces a strand of hair.

Hair follicle
The part of the dermis from which hair grows. Sebaceous glands are often connected to hair follicles.

Halo nevus
A mole with a white ring, or halo, around it. Relatively common and usually seen in children. For reasons still unknown, the immune system starts to recognize the mole as abnormal and leads to changes in the pigment of the surrounding skin. Rarely malignant (cancerous), although it should be examined carefully.

Hives see urticaria

Hydrocortisone
A low-potency topical corticosteroid used to treat skin inflammation. Available in 1% formulations without a prescription.

Hyperpigmentation
An area that is darker than the surrounding skin.

Hypopigmentation
An area that is lighter than the surrounding skin

Immune system
A complex network of specialized cells and organs that work together to defend the body against "foreign" invaders such as bacteria and viruses. In some conditions, the immune system may not function properly and may even work against the body. This leads to “autoimmune” diseases, such as arthritis and lupus.

Macule
A flat spot that appears different from the surrounding skin. Measures no more than 1cm (0.4 inches) at its greatest diameter. Smaller than a patch.

Malassezia furfur
The fungi that causes tinea versicolor. Another name for Pityrosporum folliculitis.

Melanin
The pigment in skin, created by melanosomes, that gives skin its color. Increases when the skin is exposed to ultraviolet radiation (UV rays).

Melanocytes
The cells in the dermis that create melanin.

Mohs surgery
A specialized surgery that removes a tumor (or other lesion) in stages. Each portion of removed tissue is examined under a microscope to make sure that cancerous cells have been removed while sparing as much normal skin as possible. Learn more about Mohs surgery.

Nevi
Plural form of nevus.

Nevus
A mole.

Nodule
A round, raised lesion on the skin that measures at least 1cm (0.4 inches) at its greatest diameter. Larger than a papule. If filled with fluid, referred to as a bulla. If flat, referred to as a plaque.

Onychomycosis
A fungal infection of the toenails (usually large toe) or (less commonly) the fingernails.

Papule
A raised lesion on the skin that measures no more than 1cm (0.4 inches) at its greatest diameter. Smaller than a nodule or plaque. Referred to as vesicle if filled with fluid.

Patch
A flat spot that appears different from the surrounding skin. Measures more than 1cm (0.4 inches) at its greatest diameter. Larger than a macule.

Pathology (dermatopathology)
The examination of tissue under a microscope or with other tests to determine the underlying cause of a condition, define the borders of a lesion, or measure the response to treatment.

Photoaging
The aging of skin that is accelerated from exposure to ultraviolet radiation (UV) rays from sunlight or tanning booths

Phytophotodermatitis
A rash that appears when sunlight strikes skin that has been sensitized by contact with certain plant materials. For instance, lime juice can sensitize the skin so that exposure to sun leads to a rash where the juice made contact.

Pityrosporum folliculitis
The fungi that causes tinea versicolor. Another name for Malassezia furfur.

Plaque
A flat, raised lesion on the skin that measures at least 1cm (0.4 inches) at its greatest diameter. Referred to as a nodule if rounded or dome-shaped.

Pruritus
Itching. The sensation that creates the desire to scratch or rub.

Pustule
An elevated lesion, similar to a vesicle, that contains the remnants of the body’s dead white blood cells (“pus”).

Retinoids

Retinoids are a class of medication derived from vitamin A that are used to treat a variety of skin conditions. Retinoids may be taken orally or applied onto the skin. Isotretinoin (Sotret) is an oral retinoid used for the treatment of acne. Acitretin (Soriatane) is a oral retinoid used for the treatment of psoriasis. Several topical retinoids have become the mainstay of treatment for acne, including Differin (adapalene), Epiduo (adapalene + benzoyl peroxide), Retin-A Micro (tretinoin), Tazorac (tazarotene), tretinoin, and Ziana (tretinoin +  clindamycin). Tazorac (tazarotene) is also used for the treatment of psoriasis. Renova and other topical retinoids may also be used for the treatment of aging skin. The retinoid helps to generate healthier, plumper skin cells that create a complexion with fewer fine wrinkles. Learn more about topical retinoids.

Ringworm
A fungal infection of the skin caused by a dermatophyte. Similar fungi may cause athlete’s foot or jock itch. Ringworm is not caused by a worm.

Rosacea
Rosacea is a skin disorder, formerly known as “acne rosacea” that is characterized by flushing, erythema (redness),  visible blood vessles (telangiectasias), and papules and pustules on the skin. There are several types of rosacea that are defined by the skin’s appearance. There is also a form of rosacea that affects the eyes (ocular rosacea). The pimples and pustules of rosacea respond to topical medications, such as MetroGel and Finacea, and to oral treatments, such as Oracea (doxycycline). Several of these medications are used for their anti-inflammatory effects. The redness (erythema) and the visible blood vessels of rosacea ay require treatment with laser or light therapy, such as intense pulsed light (IPL).

Sebaceous gland
The glands in the dermis that produce sebum, an oily secretion the lubricates the skin. Found most densely on the face, forehead, nose, and upper back (locations where acne most frequently develops).

Seborrhea
Excessively oily skin due to the overproduction of sebum. Increases the risk of acne or seborrheic dermatitis.

Sebum
The oil produced by sebaceous glands in the skin. Protects and moisturizes the skin.

Shingles see zoster

Skin Cancer
Skin cancer occurs when skin cells start growing abnormally, causing cancerous growths. Most skin cancers develop on the visible outer layer of the skin (the epidermis), particularly in sun-exposed areas (face, head, hands, arms, and legs). They are usually easy to detect by examining the skin, which increases the chances of early treatment and survival.

There are different types of skin cancer, each named for the type of skin cell from which they originate. Basal cell carcinoma (also called BCC) comes from the basal cells in lowest part of the epidermis. 80-85% percent of skin cancers are BCCs. Squamous cell carcinoma (also called SCC) comes from the skin cells (keratinocytes) that make up the top layers of the skin. About 10% of skin cancers are SCC. Melanoma comes from skin cells called melanocytes, which create pigment called melanin that gives skin its color. 5% of all skin cancers are melanoma. Although less common, melanoma is a very dangerous type of skin cancer and is the leading cause of death from skin disease.

Skin Tag
A skin tag is a small harmless, painless, skin-colored growth. It is commonly found on the neck and arm.

SPF
Used to measure the efficacy of sunscreens, SPF stands for “sun protection factor” and is followed by a number. The higher the number, the more the sunscreen will shield you from UVB rays, which penetrate the skin and cause tanning, burning, and increase the risk of developing skin cancer. The SPF does not reflect how well your sunscreen blocks UVA rays, which penetrate more deeply even through window glass. Exposure to UVA rays leads to premature aging of the skin , as well as some forms of skin cancer.

Squamous cell
A type of flat cell forms the surface of the skin, the lining of the hollow organs of the body (such as the bladder, kidney, and uterus), and the passages of the respiratory and digestive tracts. Keratinocytes that form the epidermis are a type of squamous cell.

Staph
Short for staphylococcus, a type of bacteria.  A common cause of skin infections, including impetigo and boils.

Sunscreen
This lotion, cream, or spray is the single most important anti-aging weapon you can buy. Sunscreen uses chemicals or physical blockers to prevent a certain percentage of ultraviolet light from getting to the skin and attacking and damaging the skin cells.

In order to guard against both UVA and UVB, you must wear a sunscreen labeled broad spectrum. Most broad-spectrum sunscreens contain the powerful UVA blocker avobenzone. However, since this ingredient breaks down after exposure to sunlight, some companies are stabilizing it with additives like Helioplex, which dramatically prolong the life span of the sunscreen. The latest UVA blocker to hit the United States is Mexoryl, which remains stable and effective even after four hours of sunlight exposure.

Steroids

Stratum corneum
The outermost layer of the epidermis that provides a protective barrier for the skin below.

Strep
Short for streptococcus, a type of bacteria. A common cause of skin infections, including folliculitis and cellulitis.

Telangiectasia
Dilated, thread-like blood vessels that appear in the skin as red or dark purple lines. Commonly occur with rosacea, aging, and other skin disorders.

Telogen
The resting phase of the hair follicle. Each hair follicle goes through a growth phase (anagen) that last several years, before a resting phase (telogen) that last several months. Finally there is the declining phase (catagen).

Telogen effluvium
Sudden, diffuse hair loss that occurs when hair is “pushed” prematurely to the resting state of telogen. Possible causes include high fevers, childbirth, severe infections, severe chronic illness, psychological stress, major surgery or illnesses, starvation, and certain medications.

Tinea capitis
A fungal infection on the head.

Tinea cruris
A fungal infection in the genital area. Also known as jock itch.

Tinea pedis
A fungal infection of the feet. Also known as athlete’s foot.

Tinea versicolor
A common, unsightly, harmless fungal infection that causes discolored patches on the skin of the back, chest, neck, and upper arms. Caused by pitysporum, also known as Malassezia furfur.

Topical
Something that is applied to the skin, such as an ointment or cream. A medication to be rubbed over a rash may be referred to as a topical medication.

Urticaria
An allergic reaction of the skin. Commonly called hives

UV Radiation
Sunlight is composed of visible light (all the colors we see in daylight), infrared radiation (which provides warmth), and ultraviolet (UV) radiation, which is carcinogenic (cancer-causing).

Varicella
The virus that causes chickenpox. It also may be reactivated years later and cause shingles.

Vesicle
A small blister that measures no more than 1cm (0.4 inches) at its greatest diameter. Smaller than a bulla. If the lesion has pus but no fluid inside, it is referred to as a papule.

Xerosis
Dry skin.

Zoster
A painful rash due to reactivation of the chickenpox virus, usually years after the initial infection. Commonly called shingles.