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A diffuse rash on the back of a human

A rash is a change of the skin that 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. 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[edit]

Common causes of rashes include:

Uncommon causes:


Skin disease Symptoms Usual area of body
Acne vulgaris Comedones, papules, pustules and nodules. Face, chest and back.
Acne rosacea Flushed appearance or redness. 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 sprinkled randomly
Erythema migrans / Lyme disease Expands over days or weeks to 5–70 cm (median 16 cm), circular or oval, red or bluish, may have an elevated or darker center, may have a central or ring-like clearing, may feel warm, not painful or itchy[4][5] Armpit, groin, back of knee, on the trunk, under clothing straps, or in children's hair, ear, or neck[6][7]
Allergic reaction Irregular, raised or flat red sores that appeared after taking medicine/drugs or eating certain foods Anywhere
Hidradenitis Suppurativa Deep sebum filled cystic condition of apocrine gland overstimulation, caused by many internal and external factors e.g., stress, toxic environmental overload and immune impairment. See Hidradenitis.
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 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 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 do not 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 Many 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
Scarlet fever Becomes confluent and forms bright red lines in the skin creases of the neck, armpits and groins (Pastia's lines) Face, chest and back, whole body, armpits, inside elbows, groins
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

Diagnostic approach[edit]

Patch test for identifying possible allergens

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, i.e. medications the patient is taking, the patient's occupation, where the patient has been and complete physical examination.[citation needed]

Points typically noted in the examination include:[citation needed]

A patch test may be ordered, for diagnostic purposes.[9]


Treatment differs according to which 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.[10]

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.[11]


  1. ^ "Eszopiclone" (PDF). F.A. Davis. 2017. Archived from the original (PDF) on October 8, 2017. Retrieved April 15, 2017.
  2. ^ "Zolpidem" (PDF). F.A. Davis. Archived from the original (PDF) on December 22, 2017. Retrieved April 15, 2017.
  3. ^ a b Fisher, Alexander A. (2008). Fisher's Contact Dermatitis. ISBN 9781550093780. Retrieved 2014-04-24.
  4. ^ "Lyme disease rashes and look-alikes". Lyme Disease. Centers for Disease Control and Prevention. Archived from the original on April 2, 2019. Retrieved April 18, 2019.
  5. ^ "Lyme disease: erythema migrans". Lyme disease NICE guideline [NG95]. National Institute for Health and Care Excellence. Archived from the original on May 9, 2019. Retrieved May 8, 2019.
  6. ^ Wright WF, Riedel DJ, Talwani R, Gilliam BL (June 2012). "Diagnosis and management of Lyme disease". American Family Physician. 85 (11): 1086–93. PMID 22962880. Archived from the original on 27 September 2013.
  7. ^ Shapiro ED (May 2014). "Clinical practice. Lyme disease" (PDF). The New England Journal of Medicine. 370 (18): 1724–1731. doi:10.1056/NEJMcp1314325. PMC 4487875. PMID 24785207. Archived from the original (PDF) on 19 October 2016.
  8. ^ 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. doi:10.1086/511637. PMID 17278064. Scholar search Archived 2021-08-29 at the Wayback Machine
  9. ^ Rebecca B. Campen M.D. (12 November 2009). The Comprehensive Guide to Skin Care: From Acne to Wrinkles, What to Do (And Not Do) to Stay Healthy and Look Your Best. ISBN 9780313378874. Archived from the original on 2023-01-14. Retrieved 2014-04-24.
  10. ^ "Hydrocortisone Topical". webmd.com. Archived from the original on 2016-03-23. Retrieved 2015-05-09.
  11. ^ "Hydrocortisone for mild inflammatory skin conditions". patient.info. Archived from the original on 2015-05-23. Retrieved 2015-05-09.

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