A Guide to Which Rashes You Should Worry About

A skin rash is something that most of us will experience at one time or another in our lives. In many cases, we will look at a rash and, even though it may be itchy and irritating, will instinctively know that it is nothing to worry about.

However, there may be times when we have a rash and will wonder if it's something serious in need of immediate—and even emergency—medical attention.

This article starts by explaining the different types of rash a person can experience. It then lists 10 different situations in which you would be strongly advised to see a healthcare provider.

Woman scratching rash

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Types of Rash

A rash is simply a change in the skin that affects its color, appearance, or texture. There are many different causes of a rash that may involve an immune system response, toxins, irritants, diseases, infections, environmental factors, or a combination of these.

Some of the more common rashes include:

  • Acne: A skin condition caused when hair follicles are blocked with oil and skin cells
  • Cellulitis: A common and potentially serious bacterial skin infection
  • Chickenpox: A highly contagious viral infection that causes an itchy, blister-like rash
  • Contact dermatitis: A rash caused by contact with certain substances
  • Diaper rash: A common rash in babies that cause bright red skin on the buttocks
  • Drug allergy: An abnormal immune reaction to a medication
  • Eczema: An inflammatory skin condition that causes a dry, itchy, scaly rash
  • Erythema multiforme: A skin disorder characterized by bullseye-shaped lesions
  • Heat rash: A rash caused by the blockage of sweat ducts
  • Herpes: A viral skin infection that can cause a blistering rash and skin ulcer
  • Hives: An abnormal immune response that causes red, itchy welts 
  • Impetigo: A highly contagious skin infection that causes red sores on the face
  • Insect bites: Including tick, flea, spider, and mosquito bites
  • Lupus erythematosus: A skin reaction caused by an autoimmune disease
  • Measles: A very contagious respiratory infection that causes a whole-body rash
  • Psoriasis: An immune-related skin disease that causes red, itchy, scaly patches
  • Ringworm: A fungal skin infection that causes a circular rash
  • Rosacea: A skin condition that causes flushing and visible blood vessels on the face
  • Scabies: A contagious, intensely itchy rash caused by tiny, burrowing mites
  • Seborrheic dermatitis: A skin condition of the scalp that causes dryness and dandruff
  • Shingles: A painful, blistering rash caused by the reaction of the chickenpox virus

There are numerous other skin rashes, both common and uncommon, that people of all ages can experience. This list of 21 skin rashes only represents a small proportion.

Signs You Need to See a Doctor for a Rash
 Verywell / Evan Polenghi

10 Signs Your Rash Requires Immediate Medical Attention

There are no hard-and-fast rules as to when you need to seek treatment for a rash. Oftentimes, you just need to follow your gut if you suspect something is unusual or wrong.

With that said, there are 10 signs that a skin rash may, in fact, be serious and requires immediate medical attention.

You Have a Fever

A fever is a common sign of an infection in which the body raises its temperature to kill a foreign invader. A rash that accompanied a fever suggests that the cause is infectious, but it may be due to a severe allergic reaction. In either instance, it is important to have it checked out immediately.

Examples include a bacterial infection called scarlet fever and a severe-whole body allergic reaction called anaphylaxis.

The Rash Covers Your Entire Body

A rash all over the body is always a cause for concern. Drug allergies commonly cause disseminated (widespread) rash, but it can also occur with Lyme disease (caused by a tick bite) or exanthems (reactive rashes mainly caused by viral infections like measles).

People who are immunocompromised (who lack immune defenses) can also have widespread rash when others might only have a localized rash. An example includes disseminated shingles in people with advanced HIV infection.

The Rash Is Painful

There is a difference between a rash being itchy and a rash being painful. Painful rashes warrant an immediate investigation as they may be the sign of a potentially serious but treatable infection like shingles or genital herpes.

In both cases, early treatment with antiviral drugs may reduce the duration and severity of the infection and, in the case of shingles, the risk of chronic nerve pain or vision damage.

You Have Difficulty Breathing

A sudden outbreak of rash or hives outbreak accompanied by shortness of breath and/or wheezing are classic symptoms of anaphylaxis. Anaphylaxis is a potentially life-threatening, whole-body allergy that requires immediate emergency care.

In addition to rash and breathing problems, symptoms of anaphylaxis may include abnormal heartbeats, diarrhea, nausea or vomiting, dizziness or fainting, and the swelling of the face, neck, or tongue.

If not treated immediately, anaphylaxis can lead to shock, coma, suffocation, heart or respiratory failure, or death.

The Rash Is Blistering

A number of rashes are characterized by the formation of blisters, both small and large. These include chickenpox, shingles, and genital herpes. All of these need to be looked at by a healthcare provider without delay.

A blistering rash can also be a sign of a potentially life-threatening drug reaction. This includes Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). Both cause skin swelling and pain in the early stages followed by widespread blistering and the peeling of the skin layers.

If left untreated, SJS and TEN can lead to shock and death due to the massive loss of fluid from open, exposed tissues.

The Rash Is Spreading Quickly

A fast-spreading rash is something you should never ignore. With some rashes, like shingles, you can sometimes watch the blistering lesions develop and spread before your eyes. The same can occur with a drug rash, which often starts on the chest and back first before spreading to the arms and finally the legs.

Arguably more concerning is a condition called cellulitis, a type of bacterial skin infection that initially starts as mildly inflamed skin but rapidly progresses, causing deep redness, swelling, warmth, and pain. As the infection spread, red streaks may begin to radiate outward accompanied by blistering or pus-filled bumps.

If not treated immediately with antibiotics, cellulitis can be fatal.

The Rash Appears Suddenly 

Many rashes appear suddenly, such as a mosquito bite or heat rash, and are not a cause for alarm. However, when the sudden outbreak is severe and widespread, it is often a sign of a severe drug reaction. Generally speaking, the faster such an outbreak occurs, the more serious it is.

With SJS and TEN, the look of the rash may also be described as being "angry," meaning that it is extremely red and painful looking. The same description may be applied to severe cases of cellulitis. In all of these situations, emergency medical care is needed.

The Rash Is Swelling or Bruising

Certain skin reactions, like hives, cause swelling due to the accumulation of fluids in the deeper layers of skin. In many cases, the swelling will resolve on its own with no harm to the tissues.

However, when the swelling is severe, you need to seek medical care immediately. This is especially true if you develop swelling of the tongue, face, or throat, all of which are signs of anaphylaxis. In cases like this, the swelling alone can block the airways and lead to suffocation and death.

A rash accompanied by bruising may be a sign of a serious condtion known as vasculitis (inflammation of blood vessels). Vasculitis limited to the skin may be the result of an infection (like a staph infection), a medication reaction (including to certain antibiotics), or an autoimmune disease (like lupus). In addition to bruising, there will often be raised bumps and reddish flat spots.

Depending on the cause, vasculitis can be mild, severe, or life-threatening.

The Rash Is Circular

 Many rashes are round, but only a handful cause a circular or coin-shaped rash, referred to as nummular lesions. There is a type of eczema called discoid eczema that falls within this category ad may require medications to resolve. Ringworm also causes a circular rash that benefits from treatment with antifungal creams or lotions.

Arguably more concern are circular "bullseye" rashes in which a central lesion is surrounded by a circular ring. A bullseye rash is characteristic of Lyme disease, an infection caused by tick bites that, if left untreated, can lead to chronic fatigue, reactive arthritis, and mood or memory problems.

Erythema multiforme can also cause a bullseye rash, usually as a result of a drug reaction. Although erythema multiforme is generally self-limiting and not usually severe, it can sometimes be a prelude to SJS and TEN and should be looked at.

The Rash Is Infected

Rashes that are eruptive (meaning that they can break open or burst) leave the underlying tissues vulnerable to bacterial infections. These types of infections are called secondary infections because they occur on top of the first (primary) infection.

People with herpes, shingles, chickenpox, eczema, and psoriasis are espeically vulnerable to this unless they make effort to keep the broken skin clean.

Symptoms of a Secondary Skin Infection

The signs of a secondary skin infection include:

  • Increasing redness, swelling, warmth, and pain at the site of the primary outbreak
  • Oozing or a pus-like discharge
  • Fever with chills
  • A secondary rash made up of red bumps with redness


A secondary infection typically requires treatment with oral and/or topical antibiotics.

Summary

There are many different types of rash ranging from mild and short-lasting to severe and life-threatening. Knowing the difference can help you determine when it is time to seek treatment for yourself or someone you know.

As a general rule, you should seek medical attention if a rash:

  • Is painful
  • Is accompanied by fever or difficulty breathing
  • Covers the entire body
  • Develops suddenly and spreads rapidly
  • Causes blistering, swelling, or bruising
  • Is circular or bullseye-shaped
  • Shows signs of infection

A Word of Verywell

If you're worried about a rash for whatever reason, it is better to be safe than sorry. Follow your gut and see your healthcare provider or go to your nearest walk-in clinic. You can also connect with a telehealth provider who can look at the rash using your smartphone or laptop camera.

If a rash is persistent or unsightly but is not causing any other troubling symptoms, ask your healthcare provider for a referral to a skin specialist, called a dermatologist, who can begin an investigation and diagnose the cause.

Frequently Asked Questions

  • How long is too long for a rash?

    Every rash is different. Generally speaking, if a rash is not severe, you should see a healthcare provider if it does not improve within a week. If a rash is severe or worsening and/or is accompanied by other symptoms (such as fever, fatigue, or dizziness), see your healthcare provider immediately.

  • How do I know if my rash is fungal or bacterial?

    Fungal skin infections like athlete's foot or ringworm usually cause a red, scaly, itchy rash. Bacterial skin infections like impetigo or cellulitis often cause hot, swollen skin with sores or blisters. Even so, rashes, swelling, redness, pain, pus, and itching are common to all skin infections and may require a dermatologist to pinpoint the cause.

16 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Heather L. Brannon, MD
Heather L. Brannon, MD, is a family practice physician in Mauldin, South Carolina. She has been in practice for over 20 years.