What Is a Skin Rash?
A rash (French rache = a sore) is any abnormal change in the skin color or texture (1).
By another definition, a rash is breaking out of the skin (eruption; exanthema in Greek) (2).
Rashes According To Size, Shape, and Consistency
A macule (Lat. macula = spot) is a small (< 1cm) skin discoloration in the level of the skin, neither raised, nor depressed, and therefore non-palpable (3).
A patch is a macule that exceeds 1cm in size (3).
A papule (Lat. papula = pimple) is a small (<1cm) palpable, raised, solid, flat skin spot (3).
A plaque is a broad (> 1cm) papule (4).
A vesicle (Lat. vesicula = small bladder) is a small (< 1cm) circumscribed, fluid-filled elevation within the upper skin layer (epidermis). It has a thin wall, and is often translucent (4).
A bulla (Lat. bulla = bubble) is a vesicle that exceeds 1cm in size.
A pustule (Lat. pustula = inflamed sore) is a pus-filled vesicle.
A crust is rough, flat or bumpy, fragile, dried secretion of the oil glands, ruptured fluid-filled skin lesions, or dried blood. It is usually red, brown or yellowish, and falls off the skin in few days or weeks in one or several pieces.
A wart (Lat. verruca) is a cauliflower-like or solid growth from the outer layer of the skin (epidermis). It is caused by virus, and they typically disappear after few months (or sometimes years) without consequences.
A nodule (from node = knob) is a palpable collection of the solid tissue in the skin, less than 1 cm in size. Nodules may arise from the skin or tissues under the skin, and may be above, in the level, or below the skin surface.
An induration is a localized hardening of the skin.
A lichenification (lichen = a flat plant that grows on rocks and trees) is a visible and palpable localized hardening of the skin and represents a chronic eczema.
A maceration (Lat. macerare = make wet) is a raw wet tissue.
An erythema (Gk. euruthema = red) refers to a skin redness that affects a localized area (> 1cm) of the skin, due to an inflammation of the skin, like in sunburn, systemic lupus erythematosus or erythema nodosum. Erythema results from dilation (widening) and congestion of the skin capillaries.
An eczema (Gk. ekzein = to erupt) refers to a localized area of inflamed skin that is red, scaly, and covered with vesicles or crusts. It is a result of an allergic or non-allergic response to skin irritation.
Hives or urticaria (Lat. urtica= nettle) is a slightly raised, pink or red, bumpy or patchy rash that usually itches. It is a symptom of an allergic reaction, mediated by a substance histamine, and represents accumulation of fluid and inflammatory cells that came out from the skin blood vessels. It may be a result of a skin irritation, or allergic reaction to foods, medicines, hair dyes or other substances.
A weal is a raised bump appearing during a skin test, if a tested person is allergic to a tested substance.
Angioedema (Gk. angio- = vessel related; oidema = swelling) is hives with swelling that occupies deep layers of the skin.
Interruption of Skin Integrity
A scratch is a punctual or linear abrasion of the upper layer (epidermis) of the skin.
A wound is a type of injury in which the skin is cut, torn or punctured.
An erosion (Lat. erodere = gnaw, eat away) is a superficial open wound, with loss of only superficial layers of the skin.
A fissure (Lat. fissura= cleft) is a linear crack in the skin, usually on the skin-mucosal junction (lips, anus).
An ulcer (Latin ulcus) is discontinuing of the skin with a localized loss of the upper skin layers (epidermis and parts of dermis).
Thick or Scald Skin
A keratosis (Gk. keras = horn) is a thickening of the uppermost layer of the skin, consisting from dead skin cells.
A scar (Lat. cicatrix) is a band or a patch of the connective fibrous tissue that replaces the normal skin after wound healing. It appears after an injury, surgical cut of the skin, burns, ulcers, acne, or other lesion where skin integrity was interrupted. Scar may get discoloured and may itch. There is no hair, oil or sweat glands in the scar. Scars are permanent changes.
A keloid (Gk. chele = claw) is a hardened area of fibrous skin that may develop from a scar, or inflammation of skin glands.
Scaling is shedding of small flakes or large patches of the upper layer (epidermis) of the skin (like in dandruff, sunburn or fungal infection of the foot).
Skin atrophy (Lat. atrophia = wasting consumption) is wasting of the skin due to local irritation, lack of nutrients, impaired blood supply, long term use of topical steroids or other causes. It may be localized or general. Hair, oil and sweat glands may be lost in the affected area.
Blood and Vessels Related Changes
Temporary Red Skin – Hyperemia
Hyperemia (Lat. hyper- = over; -emia = related to blood) is a temporary skin redness due to increased blood flow in a particular skin, or mucosal area.
Pale Skin – Pallor
Pallor (Lat. pallere = to be pale) is a skin paleness due to decreased blood flow in the skin vessels due to their narrowing. Causes of pallor include anemia, low body or external temperature, dehydration, low blood pressure, stress, tumors secreting excessive amounts of cortisol or adrenalin, and medications.
A blanching rash is a temporary white discoloration of a localized skin area after pressing on it. It is due to the blood, squeezed away from the blood vessels in the pressed area.
Blue Skin (Cyanosis)
The skin becomes blue or cyanotic (Gk. cyanos = dark blue) due to poorly oxygenated venous blood due to certain lung or heart diseases.
Bleeding is flowing of the blood out from injured vessels onto surface of the skin or mucosa (or into internal organs).
Bruise (Contusion, Hematoma)
A bruise or contusion (Lat. contusio = crushing, bruising) is accumulation of the blood under the skin, when vessels in the skin or under-skin tissues are broken, but the skin itself remains intact. Bruise is first red, then blue, and finally greenish/yellow.
An ecchimosis (Gk. ekchymosis = a pouring out) is a small (but > 1 cm) flat purplish bruise beneath the skin (or mucosa).
A purpura (Lat. purpura = purple) is a small (3mm – 1 cm) purplish bruise. It does not blanch on applying the pressure.
A petechia (Lat. petecchia (plural = petechiae) = spot on skin) is a small (< 3 mm) red or purple bruise. It does not blanch on applying the pressure.
Ecchimoses, purpurae, and petechiae are caused by trauma, or disorders of the blood or vessels.
Spider Nevus (Telangiectasia)
A spider nevus or telangiectasia (Lat. tel- = transmission over a distance; angi- = vessel related; ectasia = widening, dilation) is a small (few mm to few cm) spider-like net of tinny blood vessels, appearing under the skin anywhere on the body, but mostly on the face and upper chest. It may appear aftera sun exposure, or in alcohol abuse, liver disease, hormonal imbalance, hemangioma, or other diseases.
A tumor (Lat. tumor= swelling) refers to any swelling or overgrowth of the tissue that exceeds 1 cm in size. Tumor is NOT a synonym for cancer.
A swelling or edema (Gk. oidema= swelling) is an enlargement of the underskin tissues due to collection of the fluid (in liver, heart, kidney disease, hypothyroidism, and so on).
A bump is any small (few mm) elevation from the skin surface.
A lump is bulging of the skin, few to several centimeters in size, caused by a mass of the tissue or enclosed fluid collection within or under the skin.
A cyst (Lat. cyst = bladder, pouch) is an enclosed sac, having a distinct membrane, and clearly divided from the nearby tissue. It may contain air, fluid or a semi-solid material. A cyst usually develops from clogged sweat or oil glands or hair follicles.
A boil or abscess (Lat. abscedere = withdraw, depart) is a collection of pus within the tissue or skin, usually due to a bacterial infection. It may appear as a bulge that eventually drains to the surface.
A furuncle (Lat. furunculus = sneak thief, boil) is a small boil caused by a bacterial infection of a hair follicle.
A carbuncle (Lat. carbunculus= live coal, red tophus) is a group of furuncles that have merged together.
Nevus (plural nevi) is any chronic, benign, circumscribed hyper-pigmented lesion.
A birthmark is a blemish on the skin formed before birth, and visible at birth or few days/weeks after birth. Examples are Port-wine stain or Nevus flameus, strawbery mark, and Mongolian blue spot.
A mole is a melanocytic nevus (formed by pigment producing cells – melanocytes). It appears as a dark spot or small growth on the skin. Moles may be acquired or congenital. A beauty mark or beauty spot is a mole appearing on the face. Mongolian spot is a large, congenital, bluish discoloration on the back, appearing in Asian babies.
A lentigo (Lat. lentigo (plural lentigines) = lentile-shaped) is brown discoloration on the skin (brown nevus).
Albinism (Lat. albus = white) is a genetic disorder with a total lack of pigment melanin in the skin (white skin), eyes (red eyes) and hair (white hair).
Vitiligo – Leukoderma
Vitiligo or leukoderma (Gk. leukos = white; dermis= skin) is a chronic disorder of melanocytes that appear as multiple pale patches (depigmentation) on various parts of the body.
- Itchy Skin – Causes
- Itchy Skin – Diagnosis and Treatment
- Itchy Scalp – Pictures
- Itchy Eyes
- Itchy Face
- Itchy Throat
- Itchy Arms and Hands
- Itchy Legs
- Itchy Feet
- Hot Tub Rash
- Rash definition (nlm.nih.gov/medlineplus)
- Rash definition (medterms.com)
- James, William; Berger, Timothy; Elston, Dirk (2005) Andrews’ Diseases of the Skin: Clinical Dermatology (10th ed.). Saunders. Page 15. ISBN 0721629210.
- James, William; Berger, Timothy; Elston, Dirk (2005) Andrews’ Diseases of the Skin: Clinical Dermatology (10th ed.). Saunders. Page 16. ISBN 0721629210.
Article reviewed by Dr. Greg. Last updated on April 26, 2014