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Updated: 2017-09-02T17:53Z
A diffuse rash on the back of a male
Classification and external resources
Patient UKRash
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A rash is a change of the human 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, chapped, 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. Rash can last 5 to 20 days, the diagnosis may confirm any number of conditions. The presence of a rash may aid diagnosis; associated signs and symptoms are diagnostic of certain diseases. For example, the rash in measles is an erythematous, morbilliform, maculopapular rash that begins a few days after the fever starts. It classically starts at the head, and spreads downwards.

Differential diagnosis

Common causes of rashes include:

Uncommon causes:


Skin diseaseSymptomsUsual area of body
Acne vulgarisComedones, papules, pustules and nodules.Face, chest and back.
Acne rosaceaFlushed appearance or redness.Cheeks, chin, forehead or nose.
BoilPainful red bump or a cluster of painful red bumpsAnywhere
CellulitisRed, tender and swollen areas of skinAround a cut, scrape or skin breach
Insect biteRed and/or itchy bumps on the skinAnywhere and can be sprinked randomly
Allergic reactionIrregular, raised or flat red sores that appeared after taking medicine/drugs or eating certain foodsAnywhere
HivesBumps formed suddenlyAnywhere but usually first noticed on face
Seborrheic dermatitisBumps and swellingNear glands
Cradle CapDry, scaly skinScalp of recently born babies
Irritant contact dermatitisRed, itchy, scaly, or oily rashEyebrows, nose, edge of the scalp, point of contact with jewellery, perfume, or clothing.
Allergic Contact Dermatitis caused by poison ivy, poison oak, sumac, or Balsam of Peru[3]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 (e.g. from contaminated clothing.)
Allergic purpuraSmall red dots on the skin, or larger, bruise-like spots that appeared after taking medicineAnywhere
Pityriasis RoseaStarted 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 tanChest and abdomen
Dermatitis herpetiformisIntensely itchy rash with red bumps and blistersElbows, knees, back or buttocks
Erythema nodosumLarge red bumps that seem to bruise and are tender to touchAnywhere
PsoriasisWhite, scaly rash over red, flaky, irritated skinElbows and knees
Erythema multiformeRed, blotchy rash, with "target like" hives or sores.Anywhere
MeaslesRed rash that is raised with a fever or sore throat.Usually starts first on the forehead and face and spreads downward.
ChickenpoxMultiple blisters with a fever, cough, aches, tiredness and sore throat.Usually starts first on the face, chest and back and spreads downward.
ShinglesRed blisters that are very painful and may crustAnywhere
Fifth DiseaseStarted as a fever and then developed a bright red rashCheeks
WartsSoft bumps forming that don't itch and have no other symptomsAnywhere
RingwormBald spot on the scalp or a ring of itchy red skinAnywhere
SyphilisRash that is red but not itchyPalms of hands or soles of feet
Jock itch, yeast infection or diaper rashRed itchy rashGroin
Tinea versicolorLight coloured patchesAnywhere
ImpetigoCrusted, tan-colored soresNear nose or lip
ScabiesBite-like sores that itch and spread intenselyUsually start on hands or feet and spread everywhere
Rocky Mountain spotted feverA fine rash with a fever and headacheUsually start on arms and legs including the hands and feet
Lupus erythematosusA butterfly rash with achy jointsForehead and cheeks
Jaundice or sign of hepatitisYellowishSkin, whites of eyes and mouth
BruiseBlue or black area after being hitAnywhere
Actinic keratosesScaly, pink, gray or tan patches or bumpsFace, scalp or on the backs or the hands
Keloid or hypertrophic scarScar that has grown larger than expectedAnywhere
LipomaSoft or rubbery growthAnywhere
MiliaLots of white spotsOn the face of a baby
Molluscum or contagiosumSmall, firm, round bumps with pits in the center that may sit on tiny stalksAnywhere
Scarlet FeverBecomes confluent and forms bright red lines in the skin creases of the neck, armpits and groins (Pastia's lines)Face, chest & back, whole body, armpits, inside elbows, groins
Sebaceous cystBump with a white dome under the skinScalp, nape of the neck or upper back
Skin tagSoft, fleshy growth, lump or bumpFace, neck, armpits or groin
XanthelasmaYellow area under the skinUnder eyelids
MelanomaDark 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 itchyAnywhere
Basal cell carcinomaFleshy, growing massAreas exposed to the sun
Squamous cell carcinomaUnusual growth that is red, scaly or crustedFace, lip or chin
Kaposi's sarcomaDark or black raised spots on the skin that keep growing or have appeared recentlyAnywhere
Erythema annulare centrifugum (EAC)Pink-red ring or bullseye marksAnywhere

Diagnostic approach

The causes of a rash are numerous, which may make the evaluation of a rash extremely difficult. An accurate evaluation by a provider 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:

A patch test may be ordered, for diagnostic purposes.[5]


Treatment differs according to what rash a patient has been diagnosed with. Common rashes can be easily remedied using steroid topical creams (such as hydrocortisone) or non-steroidal treatments. Many of the medications are available over the counter in the United States.[6]

The problem with steroid topical creams i.e. hydrocortisone; is their inability to penetrate the skin through absorption and therefore not be effective in clearing up the affected area, thus rendering the hydrocortisone almost completely ineffective in all except the most mild of cases.[7]


  1. ^ "Eszopiclone" (PDF). F.A. Davis. 2017. Retrieved April 15, 2017. 
  2. ^ "Zolpidem" (PDF). F.A. Davis. Retrieved April 15, 2017. 
  3. ^ a b Fisher, Alexander A. Fisher's Contact Dermatitis. Retrieved 2014-04-24. 
  4. ^ Boyd MA, Menon P, Graves S, Gordon DL (2007). "A febrile illness with generalized papular rash involving the palms and soles". Clinical Infectious Diseases. 44 (5): 704, 755–6. PMID 17278064. doi:10.1086/511637.  Scholar search
  5. ^ Rebecca B. Campen M.D. The Comprehensive Guide to Skin Care: From Acne to Wrinkles, What to Do (And Not Do) to Stay Healthy and Look Your Best. Retrieved 2014-04-24. 
  6. ^ "Hydrocortisone Topical". 
  7. ^ "Hydrocortisone for mild inflammatory skin conditions". 

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