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Inflammatory skin disease · eczema as the thread, psoriasis alongside
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In one pass Atopic dermatitis is the most common kind of eczema.
Educational content, not medical advice — consult a clinician.
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Chapter 1
What eczema is
Atopic dermatitis is the most common kind of eczema. It starts with a skin barrier that cannot hold water: water escapes outward, irritants and allergens push inward, and the immune response then tilts toward the allergy-type inflammation called type-2 (Th2) inflammation. It is not unwashed skin, and slightly dry skin is not eczema.
Itch is the core symptom, and it is often worse at night. Flares and quiet spells alternate, so one round of cream does not end it. Infants mostly get it on the cheeks and scalp; children and adults get it in skin folds such as the inner elbows and the backs of the knees. It often travels with asthma and allergic rhinitis, but it is not a disease caused by eating, and cutting out one food will not cure it.
One situation cannot wait: if crops of small blisters or raw sores suddenly appear on eczema skin, together with fever or feeling unwell, a herpes virus may have infected the eczema (eczema herpeticum). Seek medical care immediately.
Itch is the core symptom, and it is often worse at night. Flares and quiet spells alternate, so one round of cream does not end it. Infants mostly get it on the cheeks and scalp; children and adults get it in skin folds such as the inner elbows and the backs of the knees. It often travels with asthma and allergic rhinitis, but it is not a disease caused by eating, and cutting out one food will not cure it.
One situation cannot wait: if crops of small blisters or raw sores suddenly appear on eczema skin, together with fever or feeling unwell, a herpes virus may have infected the eczema (eczema herpeticum). Seek medical care immediately.
Clinical · What eczema looks like, and its companions
Typical eczema is not a red patch you can wipe away. Its core is dryness, intense itch, and red patches or small bumps that keep coming back. Where it has flared for a long time, the skin thickens and its lines coarsen, which is called lichenification, and scratch marks are left behind. Itch is often worse at night, and it drags sleep and mood down with it.Where it appears changes with age. Infants mostly get it on the cheeks, the scalp and the outer sides of the limbs; children and adults get it in the inner elbows, behind the knees, on the neck and on the hands. Flares and quiet spells alternate. Many people whose eczema started in infancy get much better as they grow up, but the weak barrier often remains, and dryness or irritation can set it off again.
It often comes together with asthma and allergic rhinitis. This chain is called the atopic march: one allergic tendency showing up in the skin, the airways and the nose, one after another. Food allergy can also appear in the same person, but food allergy is not atopic dermatitis, and atopic dermatitis is not a disease caused by eating. The explanation now favored runs the other way: a leaky barrier lets food proteins in through the skin, and the immune system becomes sensitized to them there. A mouthful of food did not cause the eczema. This is a leading hypothesis that is still being tested.
Background · How common it is, and why it is rising
It is one of the most common chronic inflammatory skin diseases. In industrialized countries it affects up to about 20% of children and around 5% of adults. Its incidence has risen clearly over recent decades, roughly two- to three-fold, mostly in urbanized, industrialized regions (Weidinger 2018). A few decades is far too short for genes to change, so this trend suggests that environment matters as much as genes.The whole picture can be held as three forces feeding one another: a barrier that leaks water, an immune system tilted toward type-2 inflammation, and itch and scratching pushing each other up. Once you see this chain, you are less likely to be led by the claim that "cutting out one thing will cure it", and you can see why moisturizing is the foundation and when it is time to see a dermatologist.
Chapter 2
Why the skin barrier leaks
The first piece of the eczema puzzle is a fault in the stratum corneum, the outermost layer of the skin. Picture it as a brick wall: the bricks are skin cells that have flattened and lost their nuclei (corneocytes), and the mortar is a lipid mix made mostly of ceramides. When the bricks loosen and the mortar thins, water leaks out and irritants get in.
A protein that helps shape the bricks is called filaggrin. Loss-of-function mutations in its gene are the strongest known genetic risk for eczema, but carrying one does not mean you will get the disease. Low ceramides are not limited to red patches, either: skin that looks normal also runs low.
That is why repairing the barrier with moisturizer is the foundation of treatment, not an optional skincare step.
A protein that helps shape the bricks is called filaggrin. Loss-of-function mutations in its gene are the strongest known genetic risk for eczema, but carrying one does not mean you will get the disease. Low ceramides are not limited to red patches, either: skin that looks normal also runs low.
That is why repairing the barrier with moisturizer is the foundation of treatment, not an optional skincare step.
Mechanism · What the bricks and the mortar each do
The stratum corneum, the outermost layer of the skin, is easiest to picture as a brick wall. The bricks are skin cells that have died, flattened and lost their nuclei (corneocytes), stacked layer on layer; the mortar is the lipid filling the gaps, mainly ceramides plus cholesterol and free fatty acids. The bricks give mechanical protection, and the mortar does the waterproofing: it keeps water in and harmful things out (Yang 2020).Filaggrin does two jobs. It helps shape the corneocytes so the bricks are sturdy, and once it is broken down it forms natural moisturizing factor, which helps the skin hold water. Loss-of-function mutations in FLG, the gene that encodes it, are the strongest known genetic risk factor for eczema (Yang 2020). A thinner barrier lets allergens slip through the skin and stir up the immune system, so this one defect is tied both to a leaky barrier and to easier sensitization. Genes are not destiny, though: about 40% of people who carry a filaggrin mutation never develop eczema. Environment, skin care and the immune system all play a part.
Mechanism · What happens when ceramides run low
Eczema skin has clearly fewer ceramides, and not only in red, active patches: even skin that looks normal runs low (Yang 2020). The lipid molecules also have abnormal chain lengths, so the mortar cannot hold water. More water evaporates through the skin surface (transepidermal water loss), and the skin becomes drier and itchier.The barrier is not a passive covering. It is where the whole process begins. When the bricks loosen and the mortar thins, water leaks out, irritants and microbes get in, and the immune system is provoked again and again. The inflammation and the itch-scratch cycle described in Immune imbalance and the itch cycle are both built on this leaky wall.
Chapter 3
Immune imbalance and the itch cycle
Once the barrier leaks, the immune response tilts toward the allergy-type inflammation called type-2 (Th2) inflammation. Two of its signaling molecules, IL-4 and IL-13, keep taking the barrier apart while pushing the body to make allergy antibodies. Another signaling molecule, IL-31, directly stimulates the sensory nerves in the skin and sends the itch up to the brain. Psoriasis runs along a different inflammatory route.
Itch makes you scratch, scratching tears the barrier open again, and the irritated skin cells release more inflammatory signals, so the itch gets worse. Staphylococcus aureus likes to settle on this weakened skin and adds more fuel to the loop.
That is why relieving itch, repairing the barrier and scratching less are treatment goals in their own right. If the rash suddenly spreads over a large area, oozes or forms yellow crusts, think of a secondary bacterial infection and see a doctor promptly.
Itch makes you scratch, scratching tears the barrier open again, and the irritated skin cells release more inflammatory signals, so the itch gets worse. Staphylococcus aureus likes to settle on this weakened skin and adds more fuel to the loop.
That is why relieving itch, repairing the barrier and scratching less are treatment goals in their own right. If the rash suddenly spreads over a large area, oozes or forms yellow crusts, think of a secondary bacterial infection and see a doctor promptly.
Mechanism · How type-2 signals break the barrier
In eczema, inflammation points the wrong way. Instead of clearing bacteria, immune cells pour out a set of type-2 inflammatory signals tied to allergy (Weidinger 2018). IL-4 and IL-13 are at the center. They suppress filaggrin and ceramides, which keeps dismantling the barrier, and they amplify inflammation and push the body to make IgE, the allergy antibody. A worse barrier makes sensitization easier, sensitization brings more inflammation, and the two close into a vicious circle.IL-31 is known as the itch cytokine. It directly stimulates sensory nerves in the skin and carries the itch signal to the brain, which is where that gnawing itch comes from.
Guttman-Yassky 2008 compared skin biopsies from people with eczema and people with psoriasis. In eczema lesions, gene expression along the IL-23 and IL-17 pathway (the Th17/IL-23 axis) was clearly lower than in psoriasis. This is a difference measured in skin tissue. It shows that the two diseases inflame in different directions; they are not milder and stronger versions of one inflammation. The psoriasis route is covered in How psoriasis differs.
Mechanism · How the itch-scratch loop keeps turning
Itch and scratching push each other up. You itch, so you scratch; scratching tears the barrier open, and more irritants and microbes get in. The mechanically stressed skin cells then release inflammatory signals such as , IL-1 and , and the itch gets worse. The more you scratch, the more it itches, and the skin grows thicker and harder to heal. Breaking this loop (relieving itch, repairing the barrier, scratching less) is a treatment goal in its own right, not a minor thing to grit your teeth through.Eczema skin is naturally weaker at fending off bacteria, because it makes fewer of its own antimicrobial peptides. More than 90% of patients have Staphylococcus aureus living on their skin, and more of it during flares (Weidinger 2018). It does not just move in through the gap: its by-products further activate nerves and inflammation. That is why a sudden spread over a large area, oozing, or yellow crusting should raise concern about a secondary infection.
Put the three pieces together: the leaky barrier lets antigens and microbes in, type-2 inflammation pushes the response toward inflammation and itch, and itch and scratching damage the barrier again. Hitting only one link is usually not enough.
Chapter 4
How psoriasis differs
Skin inflammation is not one vague kind of heat. Eczema inflammation leans toward type-2 (Th2), and its key signals are IL-4, IL-13 and IL-31. Psoriasis runs along a different axis, the Th17/IL-23 axis: drives IL-23, and IL-23 in turn amplifies IL-17.
Guttman-Yassky 2008 compared skin biopsies from the two diseases: in eczema lesions, expression of the IL-23/IL-17 pathway was clearly lower than in psoriasis. The difference is one of direction, not degree, which is why targeted drugs for the two diseases aim at different receptors.
For the same reason, a supplement that claims to calm every kind of skin inflammation makes no sense on mechanism alone.
Guttman-Yassky 2008 compared skin biopsies from the two diseases: in eczema lesions, expression of the IL-23/IL-17 pathway was clearly lower than in psoriasis. The difference is one of direction, not degree, which is why targeted drugs for the two diseases aim at different receptors.
For the same reason, a supplement that claims to calm every kind of skin inflammation makes no sense on mechanism alone.
Clinical · Why the two rashes look opposite
The typical psoriasis lesion is a red plaque with sharp edges and a silvery-white scale, often on the outer side of the elbows and knees and on the scalp. Eczema favors skin folds and is mostly dry, itchy and oozing, the opposite pattern. IL-17 drives the skin cells of the epidermis to overgrow, and the skin's renewal cycle shrinks from a normal of about 28 days to a few days, so cells pile up as scale before they can mature (Griffiths 2021).On the eczema side there is a leaky barrier, type-2 inflammation and intense itch; on the psoriasis side there is overgrowth, Th17 inflammation and scale. The two pictures match two immune routes. They are not one inflammation treated with different ointments.
Clinical · Why psoriasis is treated as a whole-body disease
Psoriasis is a whole-body inflammatory disease, not only a skin disease. About 2-3% of people worldwide have it (Griffiths 2021). It often comes with psoriatic arthritis, cardiovascular disease, metabolic syndrome and depression. People with severe psoriasis have about a 25% higher risk of cardiovascular disease; this is an observed association, generally thought to be linked to chronic inflammation throughout the body. So it is managed as a whole-body disease, not just with a bit of ointment.Because the two immune routes differ, modern targeted drugs can aim at different points: psoriasis is treated with biologics that block IL-17 or IL-23, and eczema with dupilumab, which blocks the IL-4 receptor (see Daily care and when to see a doctor). Different inflammation means different targets, so the idea of one all-purpose anti-inflammatory supplement for every skin disease does not hold.
Chapter 5
How much diet and supplements help
For eczema, nutrition is a helper, not a switch. For people without a clear food trigger, cutting out foods is not a first-line approach: in randomized trials it improved severity only slightly, and indirect evidence suggests that removing a food completely may make a child more likely to develop a true food allergy.
Supplements are much the same. Using probiotics to treat eczema that is already there made almost no difference in a large review. Prevention is a separate question, and its evidence comes from specific trials that started in pregnancy and continued in infancy, not from routine prescribing. Vitamin D and fish oil show some signal, but they are far from being medicines.
Put most of your effort where the evidence is: repairing the barrier and controlling the inflammation.
Supplements are much the same. Using probiotics to treat eczema that is already there made almost no difference in a large review. Prevention is a separate question, and its evidence comes from specific trials that started in pregnancy and continued in infancy, not from routine prescribing. Vitamin D and fish oil show some signal, but they are far from being medicines.
Put most of your effort where the evidence is: repairing the barrier and controlling the inflammation.
Myth · Why cutting out foods is not first-line
Cutting out foods is tempting because it gives a sense of "found the culprit, back in control". Once the mechanism is clear, you can see why it mostly does not hold up, and why it can even backfire.First, the direction of cause is often backward. Eczema and food allergy do often occur together, but the mainstream explanation is that a leaky barrier (the filaggrin defect described in Why the skin barrier leaks) lets food proteins reach the immune system through the skin, where they sensitize it. Eating did not cause the eczema; the leaky barrier made sensitization easy. Dieting at the mouth often misses the real source. And food allergy is not atopic dermatitis itself.
Second, cutting out a food can create an allergy. The immune system's tolerance of foods is partly built through repeated, small exposures by mouth. If a food is removed completely just on suspicion, the body may lose the tolerance it built by mouth, and when the food comes back later, a true IgE-mediated immediate allergy (driven by allergy antibodies, with symptoms soon after eating) becomes more likely. Oykhman 2022 notes that the included trials barely measured harms, so this risk rests on indirect evidence, but it is enough to be wary of casual food elimination, especially in children.
Third, the cost is underestimated. Long-term food restriction in a child can leave protein, calcium and vitamin intake short and affect growth, and it delays treatment that actually works. In the months spent cutting out one food after another, moisturizer plus topical medicine could have brought the inflammation down.
The Oykhman 2022 pooled 10 randomized trials (599 people, mostly very young children with mild to moderate disease), and the certainty of the evidence was low: 50% of people who cut out foods improved their severity score by a clinically meaningful amount, compared with 41% of those who did not. The authors concluded that elimination may give a slight, possibly unimportant improvement. Mainstream allergy and dermatology practice also does not use food elimination as a treatment for patients without a clear food trigger. The exception is the small group with a clear trigger that repeats (a flare every time they eat it), and that needs assessment with a doctor, not deleting foods one by one at home. Put the main effort back on the foundation the evidence supports: repairing the barrier and controlling inflammation (see Daily care and when to see a doctor).
Evidence · What the supplement trials actually found
Vitamin D has the most respectable evidence among supplements, and it is still not strong. The Nielsen 2024 pooled 11 randomized trials (686 people, children and adults). Vitamin D lowered eczema severity scores (on SCORAD or EASI, two clinician-rated scales) by a small amount, and the authors say larger and longer trials are needed to confirm it. An earlier Cochrane review judged the evidence insufficient for established eczema (Bath-Hextall 2012). Taken together: it may help a little, especially in people who are low in vitamin D, but that is a long way from "vitamin D treats eczema".Fish oil (omega-3) is weaker. Two small studies suggested a possible small benefit, but they looked at many outcomes; the Cochrane review's overall conclusion was that the evidence is not enough to recommend it (Bath-Hextall 2012). Its anti-inflammatory direction is plausible, and it can be part of an overall diet, but do not expect it to control eczema on its own.
For probiotics, treatment and prevention have to be looked at separately. For treating eczema that is already there, a Cochrane review (Makrgeorgou 2018; 39 randomized trials, 2599 people) found little or no difference. Prevention is a separate line. Kalliomäki 2001 was a randomized, double-blind, placebo-controlled trial in high-risk infants (with allergic disease in the family): mothers took one Lactobacillus strain during pregnancy, and the babies took it for 6 months after birth. At age 2, eczema was about half as common in the probiotic group. That trial asked "can it prevent the disease", not "can it cure eczema that is already there". Later studies disagree; overall the idea is promising but uncertain, and it is not a routine recommendation.
A balanced diet, not running low on vitamin D, and looking after your overall inflammatory environment are all reasonable. "Cut gluten, dairy and eggs and your eczema is cured" is an overpromise that the evidence has rejected again and again.
Chapter 6
Daily care and when to see a doctor
Daily care comes down to three things: repair the leaky barrier, calm the inflammation, and avoid triggers. Moisturizers (emollients) are the foundation at every level of severity. Bathe in warm water, keep it short, and use gentle cleansers. Do not rush to blame food.
During a flare, topical steroids and topical calcineurin inhibitors (a class of steroid-free anti-inflammatory creams) are the first-line medicines. Using too little because you are afraid of steroids only lets the disease drag on. When moderate to severe disease is not controlled by standard treatment, there are targeted drugs that block the type-2 inflammatory pathway, to be used under a doctor's guidance.
If crops of small blisters or raw sores suddenly appear on eczema skin along with fever, that is an emergency: seek medical care immediately. A sudden spread over a large area, oozing or yellow crusting also needs a doctor promptly.
During a flare, topical steroids and topical calcineurin inhibitors (a class of steroid-free anti-inflammatory creams) are the first-line medicines. Using too little because you are afraid of steroids only lets the disease drag on. When moderate to severe disease is not controlled by standard treatment, there are targeted drugs that block the type-2 inflammatory pathway, to be used under a doctor's guidance.
If crops of small blisters or raw sores suddenly appear on eczema skin along with fever, that is an emergency: seek medical care immediately. A sudden spread over a large area, oozing or yellow crusting also needs a doctor promptly.
In practice · How to moisturize, and what it cannot prevent
Moisturizers (emollients) are the foundation of care that every guideline agrees on (Sidbury 2023, the American Academy of Dermatology, AAD, guideline). They act directly on the leaky brick wall described in Why the skin barrier leaks: they replace lipids, lock in water and reduce water loss through the skin surface. Use them generously and often: several times a day, and thickly within 3 minutes of a bath while the skin is still damp. Choose fragrance-free creams or ointments with simple ingredients and ceramides. Bathe in warm water, keep it short and gentle, and avoid harsh alkaline soaps, very hot water and scrubbing.Moisturizing is the foundation of treatment and maintenance, but it cannot prevent eczema from developing. The BEEP trial randomized 1,394 high-risk newborns (with a close relative who had eczema, allergic rhinitis or asthma): one group had emollient applied all over every day for the first year, and the other received standard skin-care advice only. At age 2, eczema was about as common in both groups (23% vs 25%), and the emollient group may have had slightly more skin infections (Chalmers 2020). Coating newborns in moisturizer to prevent eczema is not supported by evidence.
Common triggers include dryness and winter heating, sweat, rough fabrics (wool, synthetics), strong detergents, fragrance, dust mites and psychological stress. Get the cheap, reliable levers of environment and skin care right first, and do not rush to suspect food.
Clinical · First-line drugs and when targeted ones start
Topical corticosteroids and topical calcineurin inhibitors (such as tacrolimus, a class of steroid-free anti-inflammatory creams) are the first-line medicines for controlling flares (Sidbury 2023, AAD guideline). Used as prescribed and for a set time, topical steroids are safe and effective; using too little out of fear of steroids only lets the disease drag on.When moderate to severe disease is not controlled by standard care, modern targeted drugs work well. Dupilumab blocks the IL-4 receptor, cutting off the signals of both IL-4 and IL-13, which lands squarely on the type-2 inflammation described in Immune imbalance and the itch cycle. In two phase 3 randomized placebo-controlled trials of identical design (SOLO 1 and SOLO 2, in adults with moderate to severe disease not controlled by topical treatment), 36–38% of those on the drug were rated by their doctors as clear or almost clear after 16 weeks, compared with 8–10% on placebo (Simpson 2016). There are also topical and oral JAK inhibitors. Psoriasis has biologics that block IL-17 or IL-23 (see How psoriasis differs). Most inflammatory skin disease can now be brought under good control; the key is finding the right pathway and using the medicine properly.
Red flag · When to see a doctor soon or right away
See a doctor promptly if: sudden widespread worsening, oozing, yellow crusting, or fever — suspect secondary Staphylococcus aureus infection; sudden crops of uniform small blisters or erosions plus fever or malaise — possibly eczema herpeticum (herpes virus infecting eczema skin), an emergency needing immediate care (Weidinger 2018); whole-body redness and scaling (erythroderma), sleep or quality-of-life impact, no improvement after weeks of standard care, or significant mood impact — all warrant a dermatologist.Eczema, and inflammatory skin disease more broadly, is a chronic disease in which the barrier, the immune system, and itch and scratching all act together. It is not dirtiness, it is not something to just put up with, and it is certainly not cured by cutting out one food. The foundation is repairing the barrier with moisturizer, flares need proper medicine, and modern targeted drugs give even severe cases real options.
Disclaimer: This page is health education, not medical diagnosis or individualized treatment advice. Diagnosis and medication for eczema and psoriasis (especially topical steroids, oral drugs, and biologics) should be done under a dermatologist's guidance; if the red flags above appear, seek medical care promptly.
References · 12
- Weidinger, S., Beck, L. A., Bieber, T., Kabashima, K., & Irvine, A. D. (2018). Atopic dermatitis. Nature Reviews Disease Primers, 4(1), 1. 10.1038/s41572-018-0001-z
- Yang, G., Seok, J. K., Kang, H. C., Cho, Y. Y., Lee, H. S., & Lee, J. Y. (2020). Skin barrier abnormalities and immune dysfunction in atopic dermatitis. International Journal of Molecular Sciences, 21(8), 2867. 10.3390/ijms21082867
- Guttman-Yassky, E., Lowes, M. A., Fuentes-Duculan, J., et al. (2008). Low expression of the IL-23/Th17 pathway in atopic dermatitis compared to psoriasis. Journal of Immunology, 181(10), 7420-7427. 10.4049/jimmunol.181.10.7420
- Griffiths, C. E. M., Armstrong, A. W., Gudjonsson, J. E., & Barker, J. N. W. N. (2021). Psoriasis. The Lancet, 397(10281), 1301-1315. 10.1016/S0140-6736(20)32549-6
- Nielsen, A. Y., Hoj, S., Thomsen, S. F., & Meteran, H. (2024). Vitamin D supplementation for treating atopic dermatitis in children and adults: a systematic review and meta-analysis. Nutrients, 16(23), 4128. 10.3390/nu16234128
- Bath-Hextall, F. J., Jenkinson, C., Humphreys, R., & Williams, H. C. (2012). Dietary supplements for established atopic eczema. Cochrane Database of Systematic Reviews, 2, CD005205. 10.1002/14651858.CD005205.pub3
- Makrgeorgou, A., Leonardi-Bee, J., Bath-Hextall, F. J., et al. (2018). Probiotics for treating eczema. Cochrane Database of Systematic Reviews, 11, CD006135. 10.1002/14651858.CD006135.pub3
- Oykhman, P., Dookie, J., Al-Rammahy, H., et al. (2022). Dietary elimination for the treatment of atopic dermatitis: a systematic review and meta-analysis. Journal of Allergy and Clinical Immunology: In Practice, 10(10), 2657-2666. 10.1016/j.jaip.2022.06.044
- Kalliomäki, M., et al. (2001). Probiotics in primary prevention of atopic disease: a randomised placebo-controlled trial. The Lancet, 357(9262), 1076–1079. Double-blind RCT: Lactobacillus GG given prenatally to mothers with a first-degree relative (or partner) with atopic eczema, allergic rhinitis or asthma, and for 6 months to their infants. Atopic eczema by age 2: 15/64 (23%) vs 31/68 (46%) with placebo, RR 0.51 (0.32-0.84), NNT 4.5. One trial of one strain in high-risk infants (abstract, PMID 11297958). 10.1016/S0140-6736(00)04259-8
- Sidbury, R., Alikhan, A., Bercovitch, L., et al. (2023). Guidelines of care for the management of atopic dermatitis in adults with topical therapies. Journal of the American Academy of Dermatology, 89(1), e1-e20. 10.1016/j.jaad.2022.12.029
- Chalmers, J. R., Haines, R. H., Bradshaw, L. E., et al. (2020). Daily emollient during infancy for prevention of eczema: the BEEP randomised controlled trial. The Lancet, 395(10228), 962-972. 1394 newborns at high risk of eczema randomised to daily emollient for the first year or usual care: eczema at 2 years 23% vs 25% (adjusted RR 0.95, 0.78-1.16); skin infections in year 1 were more frequent with emollient (incidence rate ratio 1.55, 1.15-2.09). The authors advise that such families should not use daily emollients to try to prevent eczema (abstract, PMID 32087126). 10.1016/S0140-6736(19)32984-8
- Simpson, E. L., Bieber, T., Guttman-Yassky, E., et al. (2016). Two phase 3 trials of dupilumab versus placebo in atopic dermatitis. New England Journal of Medicine, 375(24), 2335-2348. 10.1056/NEJMoa1610020