How to Identify 9 Common Skin Rashes

Tips for Distinguishing One Rash From Another

A rash is a reaction in which the skin develops an abnormal texture and other features, such as pain, itching, and fluid discharge. A rash often appears in response to an allergy, toxin, infection, or larger systemic disease. The appearance can range from an almost incidental swelling of tissue to an outbreak of painful eruptive sores.

Broadly speaking, a rash can be classified as either infectious and non-infectious. Of these, there are literally hundreds of different types and thousands of possible causes. Here are 9 of the most common and tips on how to distinguish one from the other.

Urticaria; rash on arm
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There are times when an allergy or infection will cause the immune system to release a substance called histamine into the bloodstream, When this happens, tiny blood vessels in the skin will expand and leak fluid into the uppermost layer, called the epidermis The accumulation of fluid will cause the swelling we recognize as hives (urticaria).

Depending on the amount of fluid released, hives may look spongy or appear as raised areas of inflammation with no distinct border. Among other tell-tale features, hives will whiten (blanch) when you press them, can affect large areas of skin, and are often intensely itchy.

Non-itchy hives are more likely due to angioedema, a closely related condition in which the swelling occurs in deeper tissue layers.

Hives can also develop in response to hot or cold temperatures, excessive perspiration, and stress. While hives will usually go away on their own, antihistamines may be used to relieve itching and inflammation.

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Impetigo rash beneath a mans lower lip
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Impetigo is a common infection of the skin caused by either a streptococcal or staphylococcal bacteria. The most common form of impetigo, known as herpetic impetigo, occurs mostly on the face or limbs and is characterized by the eruption of tiny blisters and the formation of a honey-colored crust.

The bacteria typically enter the body through broken or abraded skin such as a cut, scrape, burn, or insect bite. Children often develop impetigo after a cold when the skin of their noses is raw, providing easy access for bacteria. 

A less common type, called bullous impetigo, leads to the formation of large blisters known as bullae. This form of impetigo is more commonly seen in newborns.

While the honey-color crust is usually the tell-tale sign of impetigo, a bacterial culture may be needed to differentiate it from other types of rash. While impetigo may cause minor itchiness, it is generally not painful (unlike shingles, scabies, or other types of eruptive lesions).

As a bacterial infection, impetigo is typically treated with antibiotics.

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Shingles

Herpes Zoster (Shingles)
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Shingles is a painful rash caused by a reactivation of the herpes zoster virus, the same virus that causes chickenpox. The lifetime risk of developing shingles can run anywhere from 10 percent to over 20 percent in some high-risk groups, including people with compromised immune systems

Shingles typically occurs later in life. It often begins with a dull, localized ache and an increased sensitivity to touch. Soon after, a distinctive cluster of tiny blisters will form, often rapidly, many of which will burst and form inflamed, crusted ulcers.

Shingles will almost always appear on one side of the body only, running along the nerve string known as a dermatome. An outbreak is typically painful, ranging in severity from a prickly, persistent discomfort to a deep, excruciating pain. If left untreated, shingles can cause long-term and sometimes permanent nerve pain known as postherpetic neuralgia.

It is important to see a doctor as soon as you recognize the characteristic, fluid-filled blisters. Early treatment with antiviral drugs such as acyclovir can shorten the duration of an outbreak and prevent the spread of the rash to vulnerable parts of the body, including the eyes.

A highly effective shingles vaccine known as Shingrix was approved by the U.S. Food and Drug Administration in October 2017. It is meant to replace Zostavax, an earlier generation vaccine, and is recommended for all adults 50 and older. 

Athlete's foot
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Athlete's foot (tinea pedis) is a common fungal infection. The characteristic symptoms include an itchy, red rash, primarily between the toes or on the soles of the feet. Symptoms can range from mild itchiness and flaking to a painful, blistering rash with fissures (skin breaks).

Athlete's foot is divided into three categories:

  • Chronic interdigital athlete’s foot (between the toes)
  • Chronic scaly athlete’s foot (largely on the soles)
  • Acute vesicular athlete’s foot (causing a blister-like infection)

Athlete's foot is easily spread in moist, unhygienic environments, such as spas and locker room floors, and typically treated with topical antifungals.

Because it is so common, athletes foot can usually be recognized by appearance alone. However, other conditions, such as plaque psoriasis and pityriasis, can cause similar symptoms and may need to be investigated if the rash does not respond to antifungal treatment.

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Skin infected with ringworm
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Ringworm (tinea corporis) is a common fungal infection that is in no way related to worms. The rash is typically round with raised, red edges. It can appear anywhere on the body but is mostly seen on arms and legs. While ringworm can cause flaking and peel, it is not inherently painful.

A related fungal condition, known as tinea capitis, involves the scalp, head, and face (particularly around hair follicles).

Ringworm is highly contagious and easily spread through skin-to-skin contact with a lesion. It can also be passed through contaminated surfaces or everyday objects such as combs, towels, doorknobs, and bedding. Pets can readily transmit the fungus.

Ringworm is typically diagnosed based on its appearance and confirmed with a microscopic examination of a skin scraping. It is important to note that other rashes can also present with annular (ring-shaped) lesions, including pityriasis rosea and ​granuloma annulare or those associated with sarcoidosis ​and lupus. Laboratory diagnosis is often vital to making the distinction.

Once diagnosed, ringworm can be effectively treated with oral or topical antifungal medications.

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Psoriasis (plaque type)
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Psoriasis is an autoimmune skin disorder characterized by a thick, scaly rash, most commonly on the front of the elbows and knees as well as the scalp. It can be triggered by stress, medication, infection, skin injury, and environmental triggers like the sun. 

For reasons not well understood, the immune system will sometimes attack its own skin cells, causing inflammation and triggering the hyperproduction of cells. The rash is formed when new skin cells are produced faster than the old ones can be shed.

The rash typically consists of thick, silvery plaques over an inflamed base of skin. The borders are usually distinct and can sometimes mimic ringworm. The scales are often very loose and can bleed when scratched.

Chronic plaque psoriasis is the most common form of psoriasis, affecting around 5 percent of the population. Other types include pustular psoriasis (characterized by pus-filled lesions) and guttate psoriasis found in children.

Psoriasis is most often diagnosed by its appearance and occasionally a skin biopsy. Because there are no blood tests that can definitively diagnose the disease, a differential diagnosis may be needed to distinguish it from similar skin rashes, such as seborrheic dermatitis, lichen planus, pityriasis, or squamous cell skin cancer.

Treatment varies by the severity of the outbreak and may include topical creams, immune suppressants, and UV light therapy. Psoriasis can often resolve spontaneously without treatment and recur just as suddenly.

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Pityriasis Rosea
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Pityriasis rosea is a common, benign rash that often begins as a single large spot on the chest, abdomen, or back, followed soon after by other smaller lesions. The lesions are typically red, scaly, and itchy.  The initial spot is often referred to as a "herald patch."

The rash is also commonly seen on the upper arm and upper leg but rarely on the face, except in children.

Pityriasis rosea can look like ringworm in the early stages with its annular, ring-like shape. Unlike ringworm, pityriasis can progress over the course of days or weeks into multiple patches. 

Other, less common forms of pityriasis include pityriasis alba (which has white, scaly flakes and mostly affects children) and pityriasis rubra pilaris (a chronic subtype with orange-red lesions and severe flaking).

Pityriasis rosea is not well understood but is believed to be caused by a virus. Because of this, there are no tests to diagnose the condition other than a physical exam. If the symptoms are severe, tests may be performed to rule out other causes, including guttate psoriasis, lichen planus, and tinea versicolor.

While treatment is typically not indicated for pityriasis rosea. a topical steroid or antihistamine may be used the rash is especially itchy.

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Red papules on the skin due to scabies
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Scabies (sarcoptic mange) is a contagious and intensely itchy skin condition caused by a tiny mite which burrows its way beneath the skin. Like head lice, it can spread quickly through schools and nursing homes and is easily passed between family members.

Scabies mimics other skin conditions such as hot tub folliculitis, seborrheic dermatitis, and pityriasis rosea. Scabies is common in people who live in crowded spaces and lack access to water or cleaning facilities. The rash most often develops on the wrists, elbow, buttocks, waist, armpits, penis, and between the fingers.

To make a definitive diagnosis, a doctor will need to scrape the affected skin and examine it under a microscope for evidence of infestation. Treatment involves the use of 5 percent permethrin cream or lotion, often in tandem with oral histamines or topical steroids to treat the rash.

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woman's mouth with Herpes simplex lesions
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Herpes simplex is a viral infection characterized by the formation of painful, open ulcers. The lesion is caused by either herpes simplex virus 1 (HSV-1), the type associated with cold sores, or HSV-2, which causes genital herpes.

Herpes can be transmitted by contact with either a sore or body fluids from an infected individual. Transmission can even occur when there are no visible lesions. Once infected, you can experience a relapse of symptoms at any time (although the first outbreak tends to be the worst)

A herpes outbreak will initially present with tingling and redness, followed by the formation of blister-like lesions that merge into an open, weeping sore. The sores can sometimes be incredibly painful and may be accompanied by fever and swollen lymph glands.

While cold sores and genital herpes may be diagnosed by appearance alone, it is possible for HSV-2 to cause a cold sore if transmitted through oral sex. The opposite is also true.

Herpes simplex can be differentiated from herpes zoster in that shingles tend to more widespread. Similar ulcers can also develop with ​primary syphilis, chancroid, and chlamydia.

If there is any doubt as to the cause of the sore, a simple test called polymerase chain reaction (PCR) can be used to confirm the presence of viral DNA.

Treatment of herpes involves the use of antiviral drugs such as acyclovir or valacyclovir.

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View Article Sources
  • Habif, T.; Campbell, J.; Chapman, M. et al. (2018) Skin Disease: Diagnosis and Treatment (3rd Edition). New York, New York: Saunders. ISBN-13:978-032307700.