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

Common causes of rashes include:

  • Food allergy
  • Medication side effects
  • Anxiety
  • 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
  • Fungal infection, such as ringworm
  • Balsam of Peru
  • 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
  • Secondary syphilis
  • Poor personal hygiene

Uncommon causes:

  • Autoimmune disorders such as psoriasis
  • Lead poisoning
  • Pregnancy
  • Repeated scratching on a particular spot
  • Lyme disease
  • Scarlet fever
  • COVID-19 (see )

Conditions

{| class="wikitable"

|-

! 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

| Armpit, groin, back of knee, on the trunk, under clothing straps, or in children's hair, ear, or neck

|-

| 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 guttate psoriasis, hand, foot and mouth disease, keratoderma blennorrhagicum);

  • Symmetry: e.g., herpes zoster usually only affects one side of the body and does not cross the midline.

A patch test may be ordered, for diagnostic purposes.

Treatment

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.

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.

References

  • Guide to rashes on Medline Plus Medical Encyclopedia – includes photographs
  • Links to pictures of skin rashes (Hardin MD/Univ of Iowa)
  • Pictures of common skin rashes compared (Dermapics)