Skip to content
How It Works
Explore
Ask a Question Resources Pricing
Who It's For
Patients
Decode results, prep for appointments, weigh options.
Caregivers & advocates
Carry the research load for someone you love.
Providers & clinicians
Resources for patients in your practice.
Log In Ask a Question
PubMed This is a summary of 21 peer-reviewed journal articles Updated
Dermatology

How Atopic Eczema is Diagnosed and Distinguished

At a Glance

Atopic eczema is diagnosed through a physical exam and medical history rather than a specific blood test. Dermatologists evaluate symptoms using clinical criteria, looking for intense itching, typical rash locations, and a personal or family history of allergies to confirm the condition.

Diagnosing atopic eczema is a specialized process because there is no single blood test or “objective” laboratory marker that can confirm it [1][2]. Instead, dermatologists use a combination of your medical history and a physical examination of your skin to build a diagnosis [1].

The Biology: A Three-Part Challenge

Atopic eczema is caused by a complex “conversation” between your genes, your immune system, and your environment.

  • The “Leaky” Barrier: Many people with atopic eczema have a genetic mutation in the filaggrin (FLG) gene [3]. Filaggrin is a protein that helps create a strong, waterproof seal on the skin’s surface. When it is weak or missing, the skin loses moisture and becomes vulnerable to irritants [4][5].
  • The Overactive Immune Response: In response to that leaky barrier, the immune system overreacts. It produces specific “messenger” proteins called cytokines—specifically IL-4 and IL-13 [6]. These cytokines drive the intense itching and redness that characterize a flare-up [7][8].
  • The Microbiome Shift: Healthy skin is covered in “good” bacteria. In atopic eczema, a “bad” bacteria called Staphylococcus aureus often takes over [9]. This overgrowth (dysbiosis) further damages the skin barrier and triggers more inflammation, creating a difficult cycle to break [10][11].

How Doctors Make the Diagnosis

Because there is no lab test, doctors use clinical frameworks like the Hanifin and Rajka criteria [12]. To meet these criteria, a patient must have at least three “major” features AND at least three “minor” features [12].
Major features include:

  1. Pruritus (intense itching) [12].
  2. Typical appearance and location (such as rashes in the folds of the elbows or knees) [12].
  3. Chronic or relapsing symptoms [12].
  4. Personal or family history of “atopy” (asthma, hay fever, or eczema) [12].

Minor features are additional signs like severely dry skin, early age of onset, or under-eye creases [12].

Differentiating Mimics

Several conditions can look like atopic eczema but require different treatments:

  • Psoriasis: While eczema is usually on the “inside” of joints (flexures), psoriasis often appears on the “outside” (extensors) like elbows and kneecaps, with thicker, silvery scales [13].
  • Allergic Contact Dermatitis (ACD): This is a reaction to a specific external trigger (like nickel or fragrance). If your eczema is only in one specific spot or doesn’t get better with standard treatment, your doctor may recommend patch testing [14]. This involves placing small amounts of potential allergens on your back for 48 hours to see if a reaction occurs [15][16].

When to Consider a Skin Biopsy

If you are over the age of 40 and develop a new, rapidly progressing, or “treatment-resistant” eczema-like rash, it is vital to speak with a dermatologist about a skin biopsy [17][18].

In some very rare cases, a type of cancer called Cutaneous T-Cell Lymphoma (CTCL) can mimic the appearance of benign eczema in its early stages [19][20]. While this cancer is quite rare, a biopsy—where a small piece of skin is removed and examined under a microscope—is the only way to accurately distinguish between a standard inflammatory condition and a malignancy [19][18]. High suspicion is especially warranted if the rash does not follow the typical “flexural” pattern or if you have no history of childhood allergies [17][21].

Back to Home

Common questions in this guide

Is there a blood test to diagnose atopic eczema?
No, there is no single blood test or laboratory marker that can confirm atopic eczema. Dermatologists diagnose the condition by physically examining your skin, evaluating your symptoms, and reviewing your detailed medical and family history.
What are the Hanifin and Rajka criteria for eczema?
The Hanifin and Rajka criteria are a clinical checklist used by doctors to diagnose atopic eczema. To be diagnosed, a patient usually needs to show at least three major features, such as intense itching and typical rash locations, along with three minor features like severely dry skin.
How do doctors tell the difference between eczema and psoriasis?
Eczema typically appears on the inside folds of joints, such as behind the knees or inside the elbows. Psoriasis, on the other hand, often develops on the outside of joints like the kneecaps and outer elbows, and is usually characterized by thicker, silvery scales.
Why might my dermatologist recommend patch testing?
If your rash is isolated to one spot or does not improve with standard treatments, it could be allergic contact dermatitis. Patch testing helps identify if your skin is reacting to a specific external trigger, such as a metal like nickel or a particular fragrance.
When is a skin biopsy necessary for an eczema-like rash?
A skin biopsy may be recommended if you are over the age of 40 and develop a new, rapidly progressing, or treatment-resistant rash. This procedure helps dermatologists rule out rare but serious conditions, such as cutaneous T-cell lymphoma, that can mimic benign eczema.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Since there is no blood test for atopic eczema, which specific clinical criteria (like Hanifin and Rajka) did you use to make my diagnosis?
  2. 2.If my eczema is not responding to standard treatments, could it be allergic contact dermatitis, and should we consider patch testing?
  3. 3.What features of my rash distinguish it from psoriasis or other similar-looking conditions?
  4. 4.Given my age, is there any reason to perform a skin biopsy to rule out more serious conditions like Cutaneous T-Cell Lymphoma?
  5. 5.Do you see signs of a Staphylococcus aureus infection or overgrowth that might be making my inflammation worse?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (21)
  1. 1

    Different definitions of atopic dermatitis: impact on prevalence estimates and associated risk factors.

    Nakamura T, Haider S, Colicino S, et al.

    The British journal of dermatology 2019; (181(6)):1272-1279 doi:10.1111/bjd.17853.

    PMID: 30822368
  2. 2

    Qualitative vs. quantitative atopic dermatitis criteria - in historical and present perspectives.

    Andersen RM, Thyssen JP, Maibach HI

    Journal of the European Academy of Dermatology and Venereology : JEADV 2016; (30(4)):604-18 doi:10.1111/jdv.13442.

    PMID: 26538253
  3. 3

    Filaggrin loss-of-function mutations and levels of filaggrin degradation products in adult patients with atopic dermatitis in Croatia.

    Jurakic Toncic R, Kezic S, Jakasa I, et al.

    Journal of the European Academy of Dermatology and Venereology : JEADV 2020; (34(8)):1789-1794 doi:10.1111/jdv.16232.

    PMID: 31989686
  4. 4

    Filaggrin mutations in relation to skin barrier and atopic dermatitis in early infancy.

    Hoyer A, Rehbinder EM, Färdig M, et al.

    The British journal of dermatology 2022; (186(3)):544-552 doi:10.1111/bjd.20831.

    PMID: 34698386
  5. 5

    The immunological and structural epidermal barrier dysfunction and skin microbiome in atopic dermatitis-an update.

    Çetinarslan T, Kümper L, Fölster-Holst R

    Frontiers in molecular biosciences 2023; (10()):1159404 doi:10.3389/fmolb.2023.1159404.

    PMID: 37654796
  6. 6

    IL-4/IL-13-Driven Dysregulation of Epidermal Lipid Metabolism in Atopic Dermatitis: An Immunometabolic Link Between Type 2 Inflammation and Barrier Dysfunction.

    Andrzejczak K, Sternak A, Witkowski W, et al.

    Cells 2026; (15(12)) doi:10.3390/cells15121130.

    PMID: 42346157
  7. 7

    Therapeutic targeting of the IL-13 pathway in skin inflammation.

    Tubau C, Puig L

    Expert review of clinical immunology 2021; (17(1)):15-25 doi:10.1080/1744666X.2020.1858802.

    PMID: 33275064
  8. 8

    Efficacy and safety of dupilumab in adults with moderate-to-severe atopic dermatitis inadequately controlled by topical treatments: a randomised, placebo-controlled, dose-ranging phase 2b trial.

    Thaçi D, Simpson EL, Beck LA, et al.

    Lancet (London, England) 2016; (387(10013)):40-52.

    PMID: 26454361
  9. 9

    Skin pH-dependent Staphylococcus aureus abundance as predictor for increasing atopic dermatitis severity.

    Hülpüsch C, Tremmel K, Hammel G, et al.

    Allergy 2020; (75(11)):2888-2898 doi:10.1111/all.14461.

    PMID: 32562575
  10. 10

    Staphylococcus aureus causes aberrant epidermal lipid composition and skin barrier dysfunction.

    Kim J, Kim BE, Berdyshev E, et al.

    Allergy 2023; (78(5)):1292-1306 doi:10.1111/all.15640.

    PMID: 36609802
  11. 11

    The prevalence of antibody responses against Staphylococcus aureus antigens in patients with atopic dermatitis: a systematic review and meta-analysis.

    de Wit J, Totté JEE, van Buchem FJM, Pasmans SGMA

    The British journal of dermatology 2018; (178(6)):1263-1271 doi:10.1111/bjd.16251.

    PMID: 29247497
  12. 12

    Systematic Review of Diagnostic Criteria Used in Atopic Dermatitis Randomized Controlled Trials.

    Vakharia PP, Chopra R, Silverberg JI

    American journal of clinical dermatology 2018; (19(1)):15-22 doi:10.1007/s40257-017-0299-4.

    PMID: 28624959
  13. 13

    Sensitive skin in patients with inflammatory chronic cutaneous disorders: results from an observational study on psoriasis, atopic dermatitis and hand eczema.

    Borghi A, Guarneri F, Pacetti L, et al.

    Italian journal of dermatology and venereology 2026; (161(2)):97-103 doi:10.23736/S2784-8671.25.08299-4.

    PMID: 41891834
  14. 14

    Patch test in Brazilian children with a clinical diagnosis of atopic dermatitis: a cross-sectional study using an extended patch test battery.

    Rigolon JR, Barbosa SS, Goudouris ES

    Allergologia et immunopathologia 2024; (52(3)):78-86 doi:10.15586/aei.v52i3.1024.

    PMID: 38721959
  15. 15

    The role of expanded series patch testing in identifying causality of residual facial dermatitis following initiation of dupilumab therapy.

    Suresh R, Murase JE

    JAAD case reports 2018; (4(9)):899-904 doi:10.1016/j.jdcr.2018.08.027.

    PMID: 30306123
  16. 16

    One-third of patients with therapy-resistant atopic dermatitis may benefit after patch testing.

    López-Jiménez EC, Marrero-Alemán G, Borrego L

    Journal of the European Academy of Dermatology and Venereology : JEADV 2019; (33(10)):e377-e378 doi:10.1111/jdv.15672.

    PMID: 31081148
  17. 17

    [Late-onset atopic dermatitis with nummular pattern].

    Pautt-Lara E, Cala-Castro L, Harris O, Villarinho AL

    Revista alergia Mexico (Tecamachalco, Puebla, Mexico : 1993) 2019; (66(4)):483-487 doi:10.29262/ram.v66i4.552.

    PMID: 32105429
  18. 18

    Dupilumab therapy in atopic dermatitis when cutaneous lymphoma is suspected: Consensus recommendations from the EORTC Cutaneous Lymphoma Tumour Group.

    Calvão J, de Masson A, Cozzio A, et al.

    The Journal of allergy and clinical immunology 2026; (157(6)):1237-1245 doi:10.1016/j.jaci.2026.04.002.

    PMID: 41967816
  19. 19

    Sezary Syndrome: A Case Report and Review of Current Therapeutics.

    Krishnan J, Thanikachalam K

    Cureus 2024; (16(4)):e58570 doi:10.7759/cureus.58570.

    PMID: 38765439
  20. 20

    Tiger-like mycosis fungoides: an unusual clinical presentation of a rare variant of mycosis fungoides.

    Ahmad A, Semkova K, Stefanato CM, et al.

    Dermatology online journal 2019; (25(7)).

    PMID: 31450281
  21. 21

    Melano-erythrodermic folliculotropic mycosis fungoides misdiagnosed as a case of recalcitrant atopic dermatitis: A case report.

    Alghamdi N, Alzammami H, Alfaraj MM

    SAGE open medical case reports 2025; (13()):2050313X251320468 doi:10.1177/2050313X251320468.

    PMID: 40083743

This page is for informational purposes only and does not replace professional medical advice. Always consult your dermatologist for an accurate diagnosis and treatment plan tailored to your specific symptoms.

Get notified when new evidence is published on atopic eczema.

We monitor PubMed for new peer-reviewed studies on this topic and email a short summary when something meaningful changes.