A rash is a change of the skin which affects its color, appearance or texture. A rash may be localized in one part of the body, or affect all the skin. Rashes may cause the skin to change color, itch, become warm, bumpy, dry, cracked or blistered, swell and may be painful. The causes, and therefore treatments for rashes, vary widely. Diagnosis must take into account such things as the appearance of the rash, other symptoms, what the patient may have been exposed to, occupation, and occurrence in family members. The diagnosis may confirm any number of conditions.
The presence of a rash may aid associated signs and symptoms are diagnostic of certain diseases. For example, the rash in measles is an erythematous, maculopapular rash that begins a few days after the fever starts. It classically starts at the head and spreads downwards.
Common causes of rashes include:
- Food Allergy
- Allergies, for example to food, dyes, medicines, insect stings, metals such as zinc or nickel; such rashes are often called hives.
- Skin contact with an irritant
- Bacterial or viral infection, e.g., by the viruses that cause chickenpox, smallpox, cold sores and measles
- Fungal infection, such as ringworm
- Reaction to vaccination
- Skin diseases such as eczema or acne
- Exposure to sun (sunburn) or heat
- Friction due to chafing of the skin
- Irritation such as caused by abrasives impregnated in clothing rubbing the skin. The cloth itself may be abrasive enough for some people
- Autoimmune disorders such as psoriasis
- Lead poisoning
- Repeated scratching on a particular spot
The causes of a rash are extremely broad, which may make the evaluation of a rash extremely difficult. An accurate evaluation by a doctor may only be made in the context of a thorough history (What medication is the patient taking? What is the patient's occupation? Where has the patient been?) and complete physical examination.
Points to note in the examination include:
- The appearance: e.g., purpuric (typical of vasculitis and Meningococcal septicemia), fine and like sandpaper (typical of scarlet fever); umbilicated lesions are typical of molluscum contagiosum (and in the past, small pox); plaques with silver scales are typical of psoriasis.
- The distribution: e.g., the rash of scarlet fever becomes confluent and forms bright red lines in the skin creases of the neck, armpits and groins (Pastia's lines); the vesicles of chicken pox seem to follow the hollows of the body (they are more prominent along the depression of the spine on the back and in the hollows of both shoulder blades); very few rashes affect the palms of the hands and soles of the feet (secondary syphilis, rickettsia or spotted fevers, guttate psoriasis, hand, foot and mouth disease, keratoderma blenorrhagica);
- Symmetry: e.g., herpes zoster usually only affects one side of the body and does not cross the midline.
- Typically, it is never a good habit for one to scratch a rash, as doing so may invigorate the rash and cause it to spread. Gently rubbing the rash may provide temporary relief, but it is more than likely better to avoid contact with the affected areas altogether.
Overview of symptoms
- Skin disease, Symptoms, Usual area of body
- Acne Rosacea Flushed appearance or Redness around cheeks, chin, forehead or nose
- Boil Painful red bump or a cluster of painful red bumps Anywhere
- Cellulitis Red, tender and swollen areas of skin Around a cut, scrape or skin breach
- Insect bite Red and/or itchy bumps on the skin Anywhere and can be sprinked randomly
- Allergic reaction Irregular, raised or flat red sores that appeared after taking medicine/drugs or eating certain foods Anywhere
- Hives Bumps formed suddenly Anywhere but usually first noticed on face
- Seborrheic dermatitis Bumps and swelling Near glands
- Cradle Cap Dry, scaly skin Scalp of recently born babies
- Irritant contact dermatitis Red, itchy, scaly or oily rash Eyebrows, nose, edge of the scalp, point of contact with jewelery, perfume or clothing.
- Allergic Contact Dermatitis caused by poison ivy, oak or sumac Red, itchy, scaly or oily rash; can also be weeping or leathery. Anywhere that came in contact with the irritant either directly or via transfer (eg. from contaminated clothing.)
- Allergic purpura Small red dots on the skin, or larger, bruise-like spots that appeared after taking medicine Anywhere
- Pityriasis Rosea Started with a single scaly, red and slightly itchy spot, and within a few days, did large numbers of smaller patches of the rash, some red and/or others tan Chest and abdomen
- Dermatitis herpetiformis Intensely itchy rash with red bumps and blisters Elbows, knees, back or buttocks
- Erythema nodosum Large red bumps that seem to bruise and are tender to touch Anywhere
- Psoriasis White, scaly rash over red, flaky, irritated skin Elbows and knees
- Erythema multiforme Red, blotchy rash, with "target like" hives or sores. Anywhere
- Measles Red rash that is raised with a fever or sore throat. Usually starts first on the forehead and face and spreads downward.
- Chickenpox Multiple blisters with a fever, cough, aches, tiredness and sore throat. Usually starts first on the face, chest and back and spreads downward.
- Shingles Red blisters that are very painful and may crust Anywhere
- Fifth Disease Started as a fever and then developed a bright red rash Cheeks
- Warts Soft bumps forming that don't itch and have no other symptoms Anywhere
- Ringworm Bald spot on the scalp or a ring of itchy red skin Anywhere
- Syphilis Rash that is red but not itchy Palms of hands or soles of feet
- Jock itch, yeast infection or diaper rash Red itchy rash Groin
- Tinea versicolor Light coloured patches Anywhere
- Impetigo Crusted, tan-colored sores Near nose or lip
- Scabies Bite-like sores that itch and spread intensely Usually start on hands or feet and spread everywhere
- Rocky Mountain spotted fever A fine rash with a fever and headache Usually start on arms and legs including the hands and feet
- Lupus erythematosus A butterfly rash with achy joints Forehead and cheeks
- Jaundice or sign of hepatitis Yellowish Skin, whites of eyes and mouth
- Bruise Blue or black area after being hit Anywhere
- Actinic keratoses Scaly, pink, gray or tan patches or bumps Face, scalp or on the backs or the hands
- Keloid or hypertrophic scar Scar that has grown larger than expected Anywhere
- Lipoma Soft or rubbery growth Anywhere
- Milia Lots of white spots On the face of a baby
- Molluscum or contagiosum Small, firm, round bumps with pits in the center that may sit on tiny stalks Anywhere
- Sebaceous cyst Bump with a white dome under the skin Scalp, nape of the neck or upper back
- Skin tag Soft, fleshy growth, lump or bump Face, neck, armpits or groin
- Xanthelasma Yellow area under the skin Under eyelids
- Melanoma Dark bump that may have started within a mole or blemish, or, a spot or mole that has changed in color, size, shape or is painful or itchy Anywhere
- Basal cell carcinoma Fleshy, growing mass Areas exposed to the sun
- Squamous cell carcinoma Unusual growth that is red, scaly or crusted Face, lip or chin
- Kaposi's sarcoma Dark or black raised spots on the skin that keep growing or have appeared recently Anywhere
- Erythema annulare centrifugum (EAC) Pink-red ring or bullseye marks Anywhere