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
Cheilitis is a medical condition characterized by inflammation of the lips. The inflammation may include the perioral skin (the skin around the mouth), the vermilion border, or the labial mucosa. The skin and the vermilion border are more common ...
, 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 The term morbilliform refers to a rash that looks like measles. The rash consists of macular lesions that are red and usually 2–10 mm in diameter but may be confluent in places. A morbilliform rash is a rose-red flat ( macular) or slightly ...
,
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
Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic derm ...
*
Medication
A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the medical field and ...
side effects
In medicine, a side effect is an effect, whether therapeutic or adverse, that is secondary to the one intended; although the term is predominantly employed to describe adverse effects, it can also apply to beneficial, but unintended, consequenc ...
*
Anxiety
Anxiety is an emotion which is characterized by an unpleasant state of inner turmoil and includes feelings of dread over anticipated events. Anxiety is different than fear in that the former is defined as the anticipation of a future threat wh ...
* 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
* Reaction to
vaccination
Vaccination is the administration of a vaccine to help the immune system develop immunity from a disease. Vaccines contain a microorganism or virus in a weakened, live or killed state, or proteins or toxins from the organism. In stimulat ...
* Skin diseases such as
eczema
Dermatitis is inflammation of the skin, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved c ...
or
acne
Acne, also known as ''acne vulgaris'', is a long-term skin condition that occurs when dead skin cells and oil from the skin clog hair follicles. Typical features of the condition include blackheads or whiteheads, pimples, oily skin, and ...
* Exposure to
sun (
sunburn) or
heat
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...
*
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction:
*Dry friction is a force that opposes the relative lateral motion of ...
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
Psoriasis is a long-lasting, noncontagious autoimmune disease characterized by raised areas of abnormal skin. These areas are red, pink, or purple, dry, itchy, and scaly. Psoriasis varies in severity from small, localized patches to comple ...
*
Lead poisoning
*
Pregnancy
Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins.
Pregnancy usually occurs by sexual intercourse, but ...
* Repeated scratching on a particular spot
*
Lyme disease
Lyme disease, also known as Lyme borreliosis, is a vector-borne disease caused by the '' Borrelia'' bacterium, which is spread by ticks in the genus '' Ixodes''. The most common sign of infection is an expanding red rash, known as erythema ...
*
Scarlet fever
*
COVID-19
Coronavirus disease 2019 (COVID-19) is a contagious disease caused by a virus, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The first known case was identified in Wuhan, China, in December 2019. The disease quick ...
(see )
Conditions
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, i.e. medications the patient is taking, the patient's occupation, where the patient has been and complete physical examination.
Points typically noted in the examination include:
* The appearance: e.g.,
purpuric (typical of
vasculitis and
meningococcal disease
Meningococcal disease describes infections caused by the bacterium ''Neisseria meningitidis'' (also termed meningococcus). It has a high mortality rate if untreated but is vaccine-preventable. While best known as a cause of meningitis, it can al ...
), fine and like sandpaper (typical of
scarlet fever); circular lesions with a central depression are typical of
molluscum contagiosum (and in the past,
small pox); plaques with silver scales are typical of
psoriasis
Psoriasis is a long-lasting, noncontagious autoimmune disease characterized by raised areas of abnormal skin. These areas are red, pink, or purple, dry, itchy, and scaly. Psoriasis varies in severity from small, localized patches to comple ...
.
* 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
Pastia's sign, Pastia lines, or Thompson's sign is a clinical sign in which pink or red lines formed of confluent petechiae are found in skin creases, particularly the crease in the antecubital fossa, the soft depression on the inside of the arm; ...
); the
vesicles of
chicken pox
Chickenpox, also known as varicella, is a highly contagious disease caused by the initial infection with varicella zoster virus (VZV). The disease results in a characteristic skin rash that forms small, itchy blisters, which eventually scab ...
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
Syphilis () is a sexually transmitted infection caused by the bacterium '' Treponema pallidum'' subspecies ''pallidum''. The signs and symptoms of syphilis vary depending in which of the four stages it presents (primary, secondary, latent, a ...
,
rickettsia or
spotted fevers,
guttate psoriasis,
hand, foot and mouth disease,
keratoderma blennorrhagicum
Keratoderma blennorrhagicum etymologically meaning keratinized (kerato-) skin (derma-) mucousy (blenno-) discharge (-rrhagia) (also called keratoderma blennorrhagica) are skin lesions commonly found on the palms and soles but which may spread to ...
);
* Symmetry: e.g.,
herpes zoster
Shingles, also known as zoster or herpes zoster, is a viral disease characterized by a painful skin rash with blisters in a localized area. Typically the rash occurs in a single, wide mark either on the left or right side of the body or fac ...
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
External links
Guide to rashes on Medline Plus Medical Encyclopedia– includes photographs
{{Authority control
Symptoms and signs: Skin and subcutaneous tissue
Dermatologic terminology