What Is It?

A rash is a temporary eruption or discoloration of the skin that is often inflamed or swollen. Rashes come in many forms and levels of severity, and they last for different periods. Some common causes of rashes include:

  • Infections — This broad category covers a wide range of illnesses, such as: viral infections (such as measles, rubella, roseola, fifth disease, varicella zoster or shingles); bacterial infections (such as impetigo, scarlet fever, Lyme disease; fungal infections, and many others.
  • Allergic reactions — These can be triggered by: medications (including antibiotics, seizure medications and diuretics); topical skin products (such as cosmetics, perfumes, skin creams); foods (especially peanuts, seafood, eggs); or insect stings (including bees, wasps, hornets).
  • Local irritants — This category includes diaper rash (caused by prolonged skin contact with urine and stool) and rashes caused by contact with harsh chemicals (such as laundry soaps, fabric softeners).
  • Plant exposure — Poison ivy, poison oak and poison sumac share a highly allergenic sap resin that can cause allergic rashes in 70 percent of people exposed to it.
  • Autoimmune disorders — This category includes systemic lupus erythematosus, dermatomyositis and scleroderma, disorders in which the body's immune defenses mistakenly attack healthy areas of the body, including the skin.


Although rash is easily recognized, all rashes are not the same. Rashes vary in their appearance, timing, location or distribution, and duration. In general, rashes may be described as macular (showing flat, red spots), papular (showing small, raised, solid bumps), macular and papular (a combination of macules and papules), papulosquamous (a combination of papules and scaly areas), and vesicular (showing small, raised, fluid-filled blisters).

Additional signs and symptoms that sometimes accompany rashes include:

  • Fever
  • Swollen lymph nodes (swollen glands)
  • Signs of a severe allergic, potentially life-threatening reaction requiring immediate emergency medical attention: difficulty breathing, hives, vomiting, abdominal cramps, rapid drop in blood pressure, confusion, unconsciousness
  • Signs of an autoimmune disorder, such as lupus (may include fatigue, poor appetite, fever, joint swelling) or dermatomyositis (often includes weak muscles, swelling and violet discoloration of the eyelids, difficulty rising after sitting)


Your doctor will take a thorough medical history, including your history of allergies and your work history (a check for exposure to chemical irritants or to patients with infections). Your doctor also may ask specific questions about your rash, including:

  • Onset — Did it appear after you ate a new food, tried a new skin care product or took a new medication?
  • Location and pattern — Does the rash affect only sun-exposed areas, or only areas in direct contact with gloves, shoes, goggles or face masks (as would be expected with allergic reactions to a chemical in the item)? Does it form a "butterfly" pattern over the cheeks and nose (a classic sign of lupus), or does it produce a bright red "slapped cheek" pattern (a sign of fifth disease)? Does it form linear streaks along the lower legs of a hiker (a sign of poison ivy)?
  • Duration — Did the rash appear and disappear within a day or two (as in roseola), or has it lasted for a week (as in fifth disease) or longer (as in SLE).
  • Occupational exposures — Is the patient a day-care worker who may be exposed to children with rash-producing illnesses (measles, rubella, roseola, fifth disease)? Does the patient work or play near wooded areas where there is increased risk of tick bites?

The doctor may suspect a specific cause for your rash based on your medical history and the history of your rash. During the physical examination, your doctor will have the opportunity to confirm these suspicions by evaluating the rash's appearance, location, pattern and any associated symptoms. In many cases, the results of your physical examination will clarify the diagnosis, and no further tests will be needed.

When additional testing is required, this may include:

  • Blood testing — Although most viral exanthems, or rashes, do not require specific identification of the virus, blood tests are available to identify some viruses and bacteria that cause rash-producing infections. Blood tests also may be performed to check for autoimmune disorders.
  • Patch tests — If your doctor suspects a local allergic reaction, he or she may conduct skin tests called patch tests. In these tests, tiny amounts of various chemicals are placed on your skin for two days. An allergic rash is looked for when the patch is removed, or one to two days later.
  • Wood's light — A Wood's lamp is a black light used to aid in evaluating rashes. Depending on the specific reason for the rash, the light may cause the affected area of skin to glow red, pale blue, yellow or white.
  • Tzanck smear — In this test, a blister is opened and scraped to obtain a laboratory sample that is checked for signs of herpes virus infection.
  • KOH preparation — In this test, a skin area that is suspected of having a fungal infection is gently scraped. Scraped material is placed on a slide and treated with KOH (potassium hydroxide) and examined under the microscope for signs of fungi.
  • Skin biopsy — In this procedure, the skin is numbed and a sample of affected skin is removed and examined in the laboratory. Stitches may be required.

Expected Duration

Although the duration of a rash depends on its cause, most rashes usually disappear within a few days. For example, the rash of a roseola viral infection usually lasts one to two days, whereas the rash of measles disappears within six to seven days. Rashes due to an antibiotic allergy may last three to 14 days, whereas diaper rash almost always clears up within one week (if diapers are changed frequently).

Rashes due to lupus or dermatomyositis may persist for an extended period of time.


Prevention depends on the cause of the rash:

  • Infections — Check that you and your children are up-to-date in your schedule of routine immunizations. Practice frequent handwashing, bathe regularly, and avoid sharing clothing or personal grooming items with other people. To prevent Lyme disease, wear light-colored clothing that contrasts with the poppy seedlike tick and covers most of your skin when you go into the woods, use approved tick repellents, and ask your doctor about your need for the newly approved Lyme immunization. Be aware that you are at an increased risk of tick exposure in areas of the country where Lyme disease is common.
  • Allergic reactions — Avoid the specific food, medicine, skin-care products or cosmetics that you have had a reaction to. Never take a medicine prescribed for someone else.
  • Irritants —For diaper rash, change diapers as soon as they become wet or soiled. Make sure that your baby's bottom is completely clean and dry before closing up the fresh diaper. For sensitivity to chemicals in cleaning products, switch to laundry soaps and fabric softeners that are free of dyes and perfumes. For irritation due to cosmetics, use hypoallergenic products that contain fewer skin-irritating preservatives and fragrances.
  • Poisonous plants — Learn to recognize poison ivy, poison oak and poison sumac. When you hike in the woods or do yard work, cover exposed arms and legs with long-sleeved shirts and long pants.
  • Insect stings — If you suspect that you are allergic to insect stings, see an allergist for testing and possible desensitization therapy. Ask your doctor about your need for a bee-sting kit, which contains emergency medication to prevent potentially life-threatening reactions.


Treatment depends on the cause of the rash:

  • Infections — Bacterial infections are treated with antibiotics, whereas fungal infections are treated with antifungal medications. Many viral infections that cause rash will resolve within several days and require no medication; less often, antiviral drugs are necessary. Avoidance when when prolonged exposure to Aspergillus.
  • Allergic reactions — A severe allergic reaction is a life-threatening medical emergency. It must be treated immediately with epinephrine, a medication that opens narrowed airways and raises dangerously low blood pressure. Localized allergic reactions can be treated with hydrocortisone cream, antihistamines and ice to relieve the itching and swelling.
  • Irritants — Diaper rash is treated with good diaper hygiene (frequent changing of soiled diapers) together with nonprescription creams or ointments that contain zinc oxide and mineral oil.
  • Prickly heat — For heat rashes caused by prolonged heat exposure, nonprescription lotions may be applied to the skin. For severe symptoms, your doctor may prescribe steroid medications to relieve discomfort and inflammation.
  • Poisonous plants — The skin should be thoroughly flushed with warm water to remove the oil soluble allergenic substance. Only then should you lather with soap and water. If you immediately take a bar of soap to your skin before flushing the skin with water, you are apt to spread the allergenic plant oil over your skin. Once you have washed off the oil, it cannot spread. The allergic dermatitis is usually treated with prescription topical steroids; however, oral steroids maybe needed for extensive rashes.
  • Autoimmune disorders — These illnesses are treated with corticosteroid and immunosuppressive drugs — medications that suppress the patient's overactive immune system.

When To Call A Professional

Seek immediate medical attention if you begin to have difficulty breathing or develop hives, a fever, a fast pulse, confusion or nausea. These could be signs of a life-threatening allergic reaction.

Always consult your doctor promptly if the rash:

  • Worsens
  • Persists beyond one week
  • Shows signs of local infection (oozing, redness or swelling of the skin)
  • Occurs together with fever, chills, swollen glands or other symptoms of infection (sore throat, cough, headache, nasal congestion, etc.)
  • Occurs together with symptoms that suggest an autoimmune disorder, such as recurring fever, malaise, fatigue, unexplained weight loss and joint swelling


In general, the prognosis for most rashes is excellent, especially after the cause has been accurately identified.

In severe allergic reactions, the patient can die within minutes without immediate medical treatment. With proper treatment, complete recovery usually occurs. Unfortunately, the patient remains at risk for future severe reactions if he is exposed to the same allergy-producing agent. For this reason, a prescription for an epinephrine-containing, self-injection pen for emergencies is usually recommended.

For long-term autoimmune conditions rash is only one of a wide variety of symptoms. The prognosis depends on the type and severity of the autoimmune disease.

Additional Info

For more information about rashes, you can contact:

National Institute of Arthritis and Musculoskeletal and Skin Diseases Information Clearinghouse
1 AMS Circle
Bethesda, MD 20892-3675
Phone: (301) 495-4484
Toll Free: (877) 226-4267
Fax: (301) 718-6366
TTY: (301) 565-2966

American Academy of Dermatology
930 North Meacham Rd.
Shaumburg, IL 60173
Phone: (847) 330-0230
Toll-free: (888) 462-3376

American Academy of Allergy, Asthma, and Immunology (AAAAI)
611 East Wells St.
Milwaukee, WI 53202
Toll-free (800) 822-2762

Food Allergy Network, The
10400 Eaton Place
Suite 107
Fairfax, VA 22030
Toll-free: (800) 929-4040
Fax: (703) 691-2713
E-Mail: mailto:fan@worldweb


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