Coronavirus Evaluation

Rash Evaluation

What is a rash evaluation? A rash evaluation is a test to find out what is causing a rash. A rash, also known as dermatitis, is an area of skin that is red, irritated, and usually itchy. A skin rash may also be dry, scaly, and/or painful. Most rashes happen when your skin touches a…

What is a rash evaluation?

A rash evaluation is a test to find out what is causing a rash. A rash, also known as dermatitis, is an area of skin that is red, irritated, and usually itchy. A skin rash may also be dry, scaly, and/or painful. Most rashes happen when your skin touches a substance that irritates it. This is known as contact dermatitis. There are two main types of contact dermatitis: allergic contact dermatitis and irritant contact dermatitis.

Allergic contact dermatitis happens when your body’s immune system treats a normally harmless substance as if it were a threat. When exposed to the substance, the immune system sends out chemicals in response. These chemicals affect your skin, causing you to develop a rash. Common causes of allergic contact dermatitis include:

  • Poison ivy and related plants, like poison sumac and poison oak. A poison ivy rash is one of the most common types of contact dermatitis.
  • Cosmetics
  • Fragrances
  • Jewelry metals, such as nickel.

Allergic contact dermatitis usually causes itching that can be severe.

Irritant contact dermatitis happens when a chemical substance damages an area of skin. This causes a skin rash to form. Common causes of irritant contact dermatitis include:

  • Household products such as detergents and drain cleaners
  • Strong soaps
  • Pesticides
  • Nail polish remover
  • Body fluids, such as urine and saliva. These rashes, which include diaper rash, most commonly affect babies.

Irritant contact dermatitis is usually more painful than itchy.

In addition to contact dermatitis, a rash may be caused by:

  • Skin disorders, such as eczema and psoriasis
  • Infections such as chicken pox, shingles, and measles
  • Insect bites
  • Heat. If you get overheated, your sweat glands can get blocked. This can cause a heat rash. Heat rashes often happen in hot, humid weather. While it can affect people of any age, heat rashes are most common in babies and young children.

Other names: patch test, skin biopsy

What is it used for?

A rash evaluation is used to diagnose the cause of a rash. Most rashes can be treated at home with over-the-counter anti-itch creams or antihistamines. But sometimes a rash is a sign of a more serious condition and should be checked by a health care provider.

Why do I need a rash evaluation?

You may need a rash evaluation if you have rash symptoms that aren’t responding to at-home treatment. Symptoms of a contact dermatitis rash include:

  • Redness
  • Itching
  • Pain (more common with an irritant rash)
  • Dry, cracked skin

Other types of rashes may have similar symptoms. Additional symptoms vary depending on the cause of the rash.

While most rashes are not serious, in some cases a rash can be a sign of a serious health condition. Call your health care provider if you or your child has a skin rash with any of the following symptoms:

Sometimes a rash can be the first sign of a severe and dangerous allergic reaction called anaphylaxis. Call 911 or seek immediate medical attention if:

  • The rash is sudden and spreads quickly
  • You have trouble breathing
  • Your face is swollen

What happens during a rash evaluation?

There are different ways to do a rash evaluation. The type of test you get will depend on your symptoms and medical history.

To test for allergic contact dermatitis, your health care provider may give you a patch test:

During a patch test:

  • A provider will place small patches on your skin. The patches look like adhesive bandages. They contain small amounts of specific allergens (substances that cause an allergic reaction).
  • You’ll wear the patches for 48 to 96 hours and then return to your provider’s office.
  • Your provider will remove the patches and check for rashes or other reactions.

There is no test for irritant contact dermatitis. But your provider may make a diagnosis based on a physical exam, your symptoms, and information you provide about your exposure to certain substances.

A rash evaluation may also include a blood test and/or a skin biopsy.

During a blood test:

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out.

During a biopsy:

A provider will use a special tool or a blade to remove a small piece of skin for testing.

Will I need to do anything to prepare for the test?

You may need to stop taking certain medicines before the test. These include antihistamines and antidepressants. Your health care provider will let you know which medicines to avoid and how long you need to avoid them before your test.

Are there any risks to the test?

There is very little risk to having a patch test. If you feel intense itching or pain under the patches once you are home, remove the patches and call your health care provider.

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

After a biopsy, you may have a little bruising, bleeding, or soreness at the biopsy site. If these symptoms last longer than a few days or they get worse, talk to your provider.

What do the results mean?

If you had a patch test and have itchy, red bumps or swelling at any of the testing sites, it means you are probably allergic to the substance tested.

If you had a blood test, abnormal results may mean you:

  • Are allergic to a certain substance
  • Have a viral, bacterial, or fungal infection

If you had a skin biopsy, abnormal results may mean you:

  • Have a skin disorder such as psoriasis or eczema
  • Have a bacterial or fungal infection

If you have questions about your results, talk to your health care provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a rash evaluation?

To relieve symptoms of a skin rash, your provider may suggest over-the-counter medicines and/or at-home treatments, such as cool compresses and cool baths. Other treatments will depend on your specific diagnosis.

References

  1. American Academy of Allergy Asthma & Immunology [Internet]. Milwaukee (WI): American Academy of Allergy Asthma & Immunology; c2020. What Makes Us Itch; [cited 2020 Jun 19]; [about 4 screens]. Available from: https://www.aaaai.org/conditions-and-treatments/library/allergy-library/what-makes-us-itch
  2. American Academy of Dermatology Association [Internet]. Des Plaines (IL): American Academy of Dermatology; c2020. Rash 101 in Adults: When to Seek Medical Treatment; [cited 2020 Jun 19]; [about 3 screens]. Available from: https://www.aad.org/public/everyday-care/itchy-skin/rash/rash-101
  3. American College of Allergy Asthma & Immunology [Internet]. American College of Allergy Asthma & Immunology; c2014. Contact Dermatitis; [cited 2020 Jun 19]; [about 4 screens]. Available from: https://acaai.org/allergies/types/skin-allergies/contact-dermatitis
  4. Cleveland Clinic [Internet]. Cleveland (OH): Cleveland Clinic; c2020. Contact Dermatitis: Diagnosis and Tests; [cited 2020 Jun 19]; [about 4 screens]. Available from: https://my.clevelandclinic.org/health/diseases/6173-contact-dermatitis/diagnosis-and-tests
  5. Cleveland Clinic [Internet]. Cleveland (OH): Cleveland Clinic; c2020. Contact Dermatitis: Overview; [cited 2020 Jun 19]; [about 3 screens]. Available from: https://my.clevelandclinic.org/health/diseases/6173-contact-dermatitis
  6. Cleveland Clinic [Internet]. Cleveland (OH): Cleveland Clinic; c2020. Contact Dermatitis: Management and Treatment; [cited 2020 Jun 19]; [about 5 screens]. Available from: https://my.clevelandclinic.org/health/diseases/6173-contact-dermatitis/management-and-treatment
  7. Familydoctor.org [Internet]. Leawood (KS): American Academy of Family Physicians; c2020. What is heat rash?; [updated 2017 Jun 27; cited 2020 Jun 19]; [about 3 screens]. Available from: https://familydoctor.org/condition/heat-rash
  8. Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998–2020. Contact dermatitis: Diagnosis and treatment; 2020 Jun 19 [cited 2020 Jun 19]; [about 3 screens]. Available from: https://www.mayoclinic.org/diseases-conditions/contact-dermatitis/diagnosis-treatment/drc-20352748
  9. Merck Manual Consumer Version [Internet]. Kenilworth (NJ): Merck & Co., Inc.; c2020. Contact Dermatitis; [updated 2018 Mar; cited 2020 Jun 19]; [about 3 screens]. Available from: https://www.merckmanuals.com/home/skin-disorders/itching-and-dermatitis/contact-dermatitis
  10. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Blood Tests; [cited 2020 Jun 19]; [about 3 screens]. Available from: https://www.nhlbi.nih.gov/health-topics/blood-tests
  11. UF Health: University of Florida Health [Internet]. Gainesville (FL): University of Florida Health; c2020. Allergy testing – skin: Overview; [updated 2020 Jun 19; cited 2020 Jun 19]; [about 2 screens]. Available from: https://ufhealth.org/allergy-testing-skin
  12. UF Health: University of Florida Health [Internet]. Gainesville (FL): University of Florida Health; c2020. Contact dermatitis: Overview; [updated 2020 Jun 19; cited 2020 Jun 19]; [about 2 screens]. Available from: https://ufhealth.org/contact-dermatitis
  13. UF Health: University of Florida Health [Internet]. Gainesville (FL): University of Florida Health; c2020. Rashes: Overview; [updated 2020 Jun 19; cited 2020 Jun 19]; [about 2 screens]. Available from: https://ufhealth.org/rashes
  14. UF Health: University of Florida Health [Internet]. Gainesville (FL): University of Florida Health; c2020. Skin lesion biopsy: Overview; [updated 2020 Jun 19; cited 2020 Jun 19]; [about 2 screens]. Available from: https://ufhealth.org/skin-lesion-biopsy
  15. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2020. Health Encyclopedia: Contact Dermatitis; [cited 2020 Jun 19]; [about 2 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=85&ContentID=P00270
  16. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2020. Health Encyclopedia: Contact Dermatitis in Children; [cited 2020 Jun 19]; [about 2 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=90&contentid=P01679
  17. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2020. Dermatology: Contact Dermatitis; [updated 2017 Mar 16; cited 2020 Jun 19]; [about 3 screens]. Available from: https://www.uwhealth.org/dermatology-skin-care/contact-dermatitis/50373
  18. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2020. Health Information: Allergy Tests: How It Is Done; [updated 2019 Oct 7; cited 2020 Jun 19]; [about 5 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/allergy-tests/hw198350.html#aa3561
  19. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2020. Health Information: Allergy Tests: How To Prepare; [updated 2019 Oct 7; cited 2020 Jun 19]; [about 4 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/allergy-tests/hw198350.html#aa3558
  20. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2020. Health Information: Allergy Tests: Risks; [updated 2019 Oct 7; cited 2020 Jun 19]; [about 7 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/allergy-tests/hw198350.html#aa3584
  21. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2020. Health Information: Skin Biopsy: Results; [updated 2019 Dec 9; cited 2020 Jun 19]; [about 8 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/skin-biopsy/hw234496.html#aa38046
  22. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2020. Health Information: Skin Biopsy: Risks; [updated 2019 Dec 9; cited 2020 Jun 19]; [about 2 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/skin-biopsy/hw234496.html#aa38044
  23. Very Well Health [Internet]. New York: About, Inc.; c2020. How Contact Dermatitis Is Diagnosed; [updated 2020 Mar 2; cited 2020 Jun 19]; [about 3 screens]. Available from: https://www.verywellhealth.com/contact-dermatitis-diagnosis-83206
  24. Very Well Health [Internet]. New York: About, Inc.; c2020. Symptoms of Contact Dermatitis; [updated 2019 Jul 21; cited 2020 Jun 19]; [about 3 screens]. Available from: https://www.verywellhealth.com/contact-dermatitis-symptoms-4685650
  25. Very Well Health [Internet]. New York: About, Inc.; c2020. What Is Contact Dermatitis?; [updated 2020 Mar 16; cited 2020 Jun 19]; [about 3 screens]. Available from: https://www.verywellhealth.com/contact-dermatitis-overview-4013705
  26. Yale Medicine [Internet]. New Haven (CT): Yale Medicine; c2020. Skin Biopsies: What You Should Expect; 2017 Nov 27 [cited 2020 Jun 19]; [about 4 screens]. Available from: https://www.yalemedicine.org/stories/skin-biopsy

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Coronavirus disease 2019 (COVID-19) is a respiratory illness that can spread from person to person. The virus that causes COVID-19 is a novel coronavirus.