Place · Level 3 · Condition

Inflammatory skin disease · eczema as the thread, psoriasis alongside

屏障 (filaggrin/神经酰胺) + 免疫失衡 (Th2 vs 银屑病 Th17) + 痒-抓循环 · 保湿是地基 · omega-3/维 D/益生菌只是温和辅助 · 忌口大多无用还有风险 · 现代药很有效

Story path

1What eczema isWhat eczema is
2Skin barrier · brick & mortarSkin barrier · brick & mortar
3Immune skew + itch-scratchImmune skew + itch-scratch
4Contrast · psoriasis' other pathContrast · psoriasis' other path
5Nutrition & supplements · honestNutrition & supplements · honest
6Barrier care + when to see a doctorBarrier care + when to see a doctor

Chapter 1

What eczema is

Eczema (medical name atopic dermatitis, AD) is not 'skin that wasn't washed clean,' nor an 'allergic constitution being dramatic.' It is a chronic disease in which the skin's outermost barrier is congenitally thin, cannot hold water, and inflames easily. The site of action is the skin barrier — the thin stratum corneum at the very surface. When the barrier leaks, water escapes outward while irritants and allergens push inward, keeping the skin chronically dry, itchy, and red.

How common it is:

One of the most common chronic inflammatory skin diseases — affecting up to 20% of children and around 5% of adults in industrialized countries (Weidinger 2018)Incidence has risen 2-3 fold over recent decades, mostly in urbanized/industrialized regions — showing environment matters, not just genes
What it typically looks like:

Core triad: dryness + intense itch + recurrent red patches/papules; chronic areas thicken with scratch marks and lichenificationItch is its defining symptom, often worse at night, badly disrupting sleep and moodLocation shifts with age: infants — cheeks, scalp, outer limbs; children and adults — the flexures (inner elbows, behind the knees), neck, hands
It is chronic and relapsing:

Marked by alternating remission and flare — not 'one cream and it's gone'Many who start in infancy improve or even 'clear' with age, but the barrier substrate often persists and can be re-ignited by dryness or irritationIt commonly travels with asthma, allergic rhinitis, food allergy — this cluster is the atopic march, one allergic tendency showing up in different organs
By the end of this island you'll have a stable frame: eczema = a leaky barrier + an inflammation-biased immune system + the itch-scratch cycle, all fueling each other. With this chain clear, you won't be led by 'cut out X and it's cured' talk, and you'll understand why moisturizing is the foundation and when to see a dermatologist.

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Chapter 2

Skin barrier · brick & mortar

The first puzzle piece of eczema is a broken skin barrier. The stratum corneum at the surface is best understood with a vivid model: a brick-and-mortar wall.

The brick + mortar model:

Bricks = dead, flattened, nucleus-free corneocytes, stacked layer on layerMortar = the lipid matrix filling the gaps — mainly ceramides + cholesterol + free fatty acidsBricks give mechanical protection; mortar does the waterproofing — keeping water in and harmful things out (Yang 2020)
Two key defects:

① Filaggrin deficiency:

Filaggrin helps shape corneocytes (makes the 'bricks' sturdy) and, once broken down, forms natural moisturizing factor that stores waterLoss-of-function mutations in the FLG gene are the single strongest known genetic risk factor for eczema (Yang 2020)It is the shared upstream of both a leaky barrier and easier allergic sensitization: a thin barrier lets allergens penetrate the skin and activate the immune systemBut genes aren't destiny: about 40% of filaggrin-mutation carriers never develop eczema — environment, care, and immune factors matter too
② Reduced ceramides (the mortar):

Eczema skin shows markedly decreased ceramides — and not only in red lesional patches; even normal-looking skin runs low (Yang 2020)Abnormal lipid chain lengths → mortar can't hold water → rising transepidermal water loss (TEWL) → drier, itchier skin
Why this step matters most: the barrier is not a passive 'skin' — it is where the whole thing starts. Loosen the bricks and thin the mortar, water escapes, irritants and microbes get in, the immune system is repeatedly provoked — the inflammation and itch-scratch cycle of the next scene are all built on this leaky wall. This is exactly why moisturizing to repair the barrier is the non-negotiable foundation of treatment, not an optional 'skincare step.'

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Chapter 3

Immune skew + itch-scratch

After the barrier leaks, the second puzzle piece is the immune system reacting in the wrong direction, and the third is the itch-scratch cycle — together they roll a small irritation into chronic inflammation.

Immune skew toward Th2 (type-2 inflammation):

AD's immune signature is Th2-dominant: immune cells pour out the signaling molecules IL-4, IL-13, IL-31 (Weidinger 2018; Yang 2020)IL-4 / IL-13 are central: they further damage the barrier (suppressing filaggrin and ceramides), amplify inflammation, and drive IgE production — forming a vicious loop of broken barrier → easier sensitization → more inflammation → worse barrierIL-31 is the 'itch cytokine': it directly stimulates sensory nerves in the skin, sending itch signals to the brain
The itch-scratch cycle:

Itch → scratch → the barrier is torn → more irritants/microbes enter + mechanically stressed keratinocytes release pro-inflammatory tumor necrosis factor alpha: A strong pro-inflammatory signal molecule that runs high in chronic inflammation., IL-1, interleukin-6: A pro-inflammatory signal molecule (cytokine) released by immune cells during inflammation. → more itch (Yang 2020)A self-reinforcing loop: the more you scratch the more it itches, the skin thickening and becoming harder to healBreaking this loop (relieve itch + repair barrier + don't scratch) is itself a major treatment goal, not a matter of 'just tough it out'
The microbial link — Staphylococcus aureus:

Eczema skin is congenitally weak at self-defense (reduced antimicrobial peptides); over 90% of patients have skin colonized by Staphylococcus aureus, more so during flares (Weidinger 2018)It doesn't just 'move into an opening': its metabolites further activate nerves and inflammation, adding fuel to the itch-scratch cycleThis is why sudden widespread worsening, oozing, or yellow crusting should raise concern for secondary infection (see the red flags in the last scene)
Putting the three pieces together: the leaky barrier (previous scene) lets antigens and microbes in, Th2 immunity pushes the response toward inflammation and itch, and itch-scratch damages the barrier again. All three connect head to tail — which is why eczema is chronic and relapsing, and why hitting only one link (moisturizer alone, or one supplement) is usually not enough.

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Chapter 4

Contrast · psoriasis' other path

Inflammatory skin disease is more than eczema. Placing eczema next to psoriasis helps you grasp something important: skin inflammation is not a vague 'internal heat' — different diseases run down different immune pathways, so their treatments differ too.

Both chronic inflammatory skin diseases, yet opposite immune directions:

Eczema: Th2-dominant (IL-4 / IL-13 / IL-31) — a leaky, dry, intensely itchy barrier (previous scene)Psoriasis: driven mainly by the Th17 / IL-23 axis — a vicious amplifying loop of tumor necrosis factor alpha: A strong pro-inflammatory signal molecule that runs high in chronic inflammation. → IL-23 → IL-17 (Guttman-Yassky 2008; Griffiths 2021)Head-to-head studies found the IL-23 / IL-17 pathway is markedly lower in eczema skin than in psoriasis (Guttman-Yassky 2008) — not a difference of degree but of direction
Appearance matches mechanism:

Psoriasis' classic lesion is well-demarcated red plaques with silvery-white scale, often on the extensor elbows/knees and scalp — the opposite of eczema's flexural, dry-itchy-oozing patternIL-17 drives keratinocyte over-proliferation, compressing skin turnover from a normal ~28 days to a few days → immature cells pile up as scale
Psoriasis is a systemic inflammatory disease, not just skin:

Prevalence is about 2-3% of the global population (Griffiths 2021)It commonly co-occurs with psoriatic arthritis, cardiovascular disease, metabolic syndrome, depression; severe psoriasis raises cardiovascular risk by about 25%, tied to chronic systemic inflammation (Griffiths 2021)So psoriasis is managed as a systemic disease, not merely 'a bit of ointment'
Why this contrast matters: precisely because the two immune roads differ, modern targeted drugs can hit precisely — psoriasis responds well to anti-IL-17 / IL-23 biologics, while eczema uses the anti-IL-4-receptor drug dupilumab (see the last scene). Once you understand 'different inflammation, different targets,' you see why 'one universal anti-inflammatory supplement cures all skin disease' is an unsupported claim.

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Chapter 5

Nutrition & supplements · honest

Can you eat your way out of eczema? This is the most-asked and most-overstated question. The honest answer: nutrition and supplements play a modest, supportive, person-dependent role — not the lead — while blind food elimination is mostly useless and can backfire.

Supplements: some signal, but not drugs

① Vitamin D — the most presentable evidence, still not strong:

A 2024 meta-analysis (11 RCTs, 686 people) found supplementation gives a small reduction in severity scores (SCORAD/EASI) (Nielsen 2024)But an earlier Cochrane review judged the evidence insufficient for established eczema (Bath-Hextall 2012) — together the takeaway is 'possibly a little help, especially if you're deficient,' far from 'vitamin D treats eczema'
② Omega-3 (fish oil) — mixed, on the weak side:

Some small studies suggest less inflammation and itch; others show no difference; Cochrane concluded the evidence is insufficient to recommend it (Bath-Hextall 2012)The anti-inflammatory direction is reasonable as part of an overall healthy diet, but don't expect it to control eczema alone
③ Probiotics — nearly useless for treatment, controversial for prevention:

For treating existing eczema: a Cochrane review (39 RCTs, 2599 people) found little to no difference (Makrgeorgou 2018)For prevention (pregnancy/infancy): an early RCT (Kalliomäki 2001) suggested lower incidence in high-risk infants, but later trials disagree, and multi-strain may beat single-strain — overall 'promising but uncertain,' not a routine recommendation
Elimination diets: mostly unhelpful, and risky

A meta-analysis (10 RCTs, 599 people): elimination gives only a small, possibly clinically unimportant improvement in severity (Oykhman 2022)The real risk: blind elimination may itself trigger IgE-mediated food allergy — turning a skin problem into a real allergy; in children it can also cause malnutrition and delay more effective treatment (Oykhman 2022)Major allergy and dermatology guidelines do not recommend elimination diets as an eczema treatmentException: a minority have a clear, reproducible food trigger (flare each time they eat it); that should be assessed with a doctor, not by self-imposed 'cut this and that'
This scene's stance: nutrition is a helper for eczema, not a switch. A balanced diet, not being vitamin-D deficient, and tending the overall inflammatory environment are reasonable; but 'cut gluten/dairy/eggs and cure eczema' is an overpromise the evidence repeatedly rejects. Spend the energy you'd waste on elimination diets on the next scene's barrier-repairing moisturization — the payoff is far larger.

Why elimination diets are both weak and risky

Elimination diets are tempting because they give a feeling of 'found the culprit, back in control.' But once the mechanism is clear, you see why they mostly don't hold up and can even backfire.

First, the causal direction is often reversed. Eczema and food allergy do co-occur, but the mainstream explanation is: a leaky barrier (the filaggrin defect from scene two) lets food proteins reach the immune system through the skin and get sensitized — meaning it isn't 'eating caused eczema,' but 'eczema's leaky barrier makes sensitization easy.' So dieting at the mouth often misses the true upstream.

Second, eliminating can create allergy. Immune tolerance to foods is partly built by repeated, small oral exposure. Pull a suspected food out entirely on suspicion, and the body may lose that oral tolerance; when reintroduced later, true IgE-mediated immediate allergy becomes more likely (Oykhman 2022). This is why turning eczema into a food allergy 'by eating' is a real risk, especially in children.

Third, the cost is underrated. Long-term elimination in a child risks inadequate protein, calcium, and vitamins, affecting growth — while delaying genuinely effective treatment: during those months of 'cut this and that,' moisturizers plus topicals could have suppressed the inflammation.

So the honest path is: don't treat elimination as therapy. If you truly suspect a food (reproducible flares within hours of eating it), record it and take it to a doctor for a proper work-up (oral food challenge if needed), rather than deleting foods one by one at home. Put the main effort back on the evidence-based foundation — repair the barrier + control inflammation (next scene).

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Chapter 6

Barrier care + when to see a doctor

Collapsing the earlier mechanisms into a practical path: the core of eczema isn't 'find one miracle remedy' but 'repair the leaky barrier, suppress the inflammation, avoid the triggers.'

Step 1 · Moisturize to repair the barrier (the foundation, at any severity):

Emollients/moisturizers are the care foundation every guideline agrees on (Sidbury 2023 AAD) — they directly address scene two's leaky 'brick wall': replacing lipids (mortar), locking in water, reducing transepidermal water lossApply generously and frequently: many times daily, and thickly within 3 minutes of bathing while skin is still damp; choose fragrance-free, simple, ceramide-containing creams/ointmentsBathe with warm (not hot), short, gentle routines; avoid harsh alkaline soaps and scrubbingAn important clarification: moisturizing is the foundation of treatment and maintenance, but it cannot prevent eczema from developing — the large BEEP trial (1,394 high-risk infants) found that daily all-over emollient from birth did not prevent eczema and may slightly raise skin infections (Chalmers 2020). So 'slather newborns in oil to prevent eczema' is not evidence-supported
Step 2 · Avoid triggers:

Common triggers: dryness/winter heating, sweat, rough fabrics (wool/synthetics), harsh detergents, fragrance, dust mites, psychological stressDon't rush to blame food (see previous scene): first get the high-value levers of environment and skin care right
Step 3 · Medication (when needed, doctor-guided):

Topical corticosteroids (TCS) and topical calcineurin inhibitors (TCI, e.g. tacrolimus) are first-line for controlling flares (Sidbury 2023 AAD). Correct, time-limited topical steroid use is safe and effective; under-treatment from 'steroid phobia' actually lets the disease drag onFor moderate-to-severe disease uncontrolled by standard care, modern targeted drugs are highly effective: dupilumab (anti-IL-4-receptor, precisely hitting scene three's Th2 pathway) significantly improved disease in two phase-3 trials (Simpson 2016); also topical/oral JAK inhibitorsPsoriasis has anti-IL-17 / IL-23 biologics (scene four). All of this shows: inflammatory skin disease is now highly treatable — the key is targeting the right pathway with proper medication
Red flags — see a doctor (promptly):

Sudden widespread worsening, oozing, yellow crusting, fever → suspect secondary Staphylococcus aureus infectionSudden crops of uniform small blisters/erosions + fever/malaise → possibly eczema herpeticum (herpes virus infecting eczema skin), an emergency needing immediate care (Weidinger 2018)Whole-body redness and scaling (erythroderma), sleep/quality-of-life impact, no improvement after weeks of standard care, or significant mood impact → all warrant a dermatologist
This island's core stance: eczema (and inflammatory skin disease broadly) is a chronic disease of barrier + immunity + itch-scratch together — not 'dirtiness,' not 'endure it,' and certainly not 'cut one food and cure it.' The foundation is barrier-repairing moisturization, flares need proper medication, and modern targeted drugs give even severe cases an answer. With this chain understood, you won't be swept away by overpromises, and you'll know when to hand it to a doctor.

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.

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