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Mold and Psoriasis: What Is Established and What Is Not
Last revised 2026-09-05
The short answer
This is the thinnest evidence base of any topic on this site, and it is also the one with the most money circulating around it. So let us separate the parts.
Reasonably well established:
- Mould in water-damaged buildings produces mycotoxins, and several of those mycotoxins act on immune pathways that are central to psoriasis — Th17 activation, gut barrier damage, skin barrier damage, and destruction of regulatory T cells.
- People differ genetically in how well they clear these compounds, and some of that variation has been associated with psoriasis risk.
- Essentially everyone has measurable mycotoxin exposure from food, independent of any building.
Not established:
- That mould causes psoriasis.
- That remediating a building, or taking binders, clears psoriasis. No randomised trial has tested this.
- That a positive urine mycotoxin test means you have a clinical mould problem. It does not, and the book says so itself.
If you take one practical thing away: test the building before you test yourself, and test yourself before you buy anything. The order matters, and the sequence in the wrong direction is how people spend thousands of dollars on the wrong problem.
And whatever you find, this is not a reason to stop or change a prescribed psoriasis treatment.
Why a building could plausibly matter
Chapter 9 of Heal Psoriasis opens with the scale of the problem. A US Environmental Protection Agency survey begun in 1994 inspected over 100 commercial buildings: 85% had experienced water damage at some point, and 45% had active leaks. The WHO estimates that living or working in a damp, mould-contaminated building raises respiratory illness risk by 75%.
Mould itself is not the mechanism. The mechanism is what mould produces — mycotoxins, which are molecules rather than organisms. Chapter 9 singles out four, and each hits a different part of psoriasis biology:
- Ochratoxin A (from Aspergillus and Penicillium) activates the Th17 pathway — the same pathway biologics like secukinumab and ixekizumab are built to shut down. Recent work describes it doing this by manipulating STAT3 signalling and suppressing the SOCS proteins that normally restrain Th17.
- Trichothecenes (from Stachybotrys, the "black mould") damage the intestinal lining at concentrations below regulatory limits — which routes straight into the gut permeability story.
- Fumonisins inhibit ceramide synthase. Ceramides hold skin cells together; less ceramide means a weaker skin barrier.
- Gliotoxin (from Aspergillus fumigatus) selectively kills regulatory T cells — the cells whose job is to stop autoimmune reactions.
Between them: Th17 up, gut barrier down, skin barrier down, Tregs dead. That is a coherent story, and all four can come from one building.
But hold the strength of that evidence in view. These are mechanistic, cell-culture and animal findings about what mycotoxins do to immune pathways. They are not trials of mould-exposed psoriasis patients. A plausible mechanism is a reason to investigate, not a diagnosis.
Why two people in the same house get different outcomes
Chapter 9's answer is genetics, in two layers.
Presentation. The HLA system determines how immune cells display foreign molecules for inspection. Certain HLA variants present mycotoxins poorly — the immune system never gets shown the wanted poster, and the toxins circulate without being recognised or cleared.
Elimination. Glutathione S-transferase (GST) enzymes attach glutathione to toxic molecules so the kidneys can flush them. Some people are missing entire GST genes. Chapter 9 cites a 2018 study in Indian psoriasis patients: missing GSTT1 was associated with a 2.74-fold higher psoriasis risk, missing GSTM1 with 1.58-fold. An Italian study put the "double null" genotype at 5.94-fold.
The book then does something worth crediting: it immediately caveats its own numbers. GST associations vary between populations, and a Turkish study did not find the same strength of association. The broad pattern — detoxification capacity matters — shows up across studies; the specific effect sizes do not travel well.
CIRS, Shoemaker, and the "one in four" number
Ritchie Shoemaker described Chronic Inflammatory Response Syndrome (CIRS) — a framework for biotoxin illness in people who cannot clear the toxins — and identified HLA-DR haplotypes he associated with that failure. Chapter 9 reports that in his patient cohorts, roughly one in four carried susceptible haplotypes.
The book then says the following, and it is the most important sentence in the chapter:
The full CIRS model hasn't been validated in large, independent, multi-center trials. The "one in four" susceptibility figure comes from clinical observation, not population-level epidemiology.
Hold onto that, because Chapter 5 of the same book states flatly that "about 25% of the population carries specific HLA gene variants that prevent them from normally clearing certain biotoxins." Those two passages are not compatible. Chapter 9's version is the careful one and the one to trust. Chapter 5 restates a clinic-derived observation as a population statistic. If you have read that figure quoted anywhere as an established prevalence, this is where it comes from, and it is not one.
Chapter 9's position — that Shoemaker's work is clinically useful, partly supported by brain imaging and gene expression findings, and under-investigated rather than disproven — is defensible. "Weak evidence doesn't mean it's false" is a fair thing to say. It is also not a licence to spend money as though the question were settled.
Everyone is already exposed. This is the part that protects you.
The BIOMYCO study tested urine from 239 adults in Belgium. 100% tested positive for deoxynivalenol, a trichothecene. More than half tested positive for ochratoxin A. Not a high-risk subgroup — everyone tested.
A 2020 review estimated that 60 to 80% of global food crops contain detectable levels of at least one mycotoxin. Cereals, dried fruit, coffee, wine, spices and nuts are the most commonly contaminated.
The consequence is the single most useful fact on this page, and Chapter 9 states it directly: a positive urine mycotoxin test does not automatically mean you have a clinical problem. Nearly everyone excretes some. What matters is the level, the context, and whether you have a genetic reason not to clear them.
If somebody sells you a urine panel, gets a positive, and moves straight to a treatment plan without any of that context, they have sold you a test that was always going to come back positive.
Should you suspect this at all?
Chapter 9 gives a pattern rather than a test. Suspect an environmental driver if:
- Your psoriasis appeared or worsened after moving to a new home or workplace
- The building has a history of water damage, leaks, or a musty smell
- You have symptoms beyond your skin — chronic fatigue, brain fog, joint pain, sinus problems, frequent headaches, light sensitivity, unusual thirst
- You have already done the diet, supplement and stress work with limited improvement
- You have a known mould exposure in your history
- You work in agriculture, mining or industrial settings
The last one is the honest signal: this chapter is aimed at people for whom the rest of the book did not work. It is a troubleshooting chapter, not a starting point. Chapter 20 lists mould among the "hidden blockers" for exactly that reason.
What to actually do, in order
1. Test the building, not the body. ERMI testing (Environmental Relative Moldiness Index) uses dust samples to identify 36 indoor mould species; kits are ordered online and mailed to labs. The book gives a score above 5 as suggesting significant contamination. A certified indoor environmental professional goes further with moisture meters, thermal imaging and air sampling, and finds things dust tests miss — mould inside walls or in HVAC systems.
An ERMI score is a prompt to investigate. It is not a diagnosis of anything about you.
2. Then test yourself, if the building justifies it. Urinary mycotoxin panel (with the interpretation caveat above), HLA-DR typing, and heavy metal testing. Chapter 9 also lists inflammatory markers — TGF-beta1, C4a, MSH, VIP, VEGF — while noting they are not specific to mould.
3. Remove the exposure. The book is honest that this is the hardest step and the most important one. Proper remediation is not a bleach-and-paint job: it means finding the moisture source, removing contaminated materials, decontaminating and fixing the water intrusion. Some people end up leaving buildings entirely, which the book acknowledges is an enormous decision with financial and social consequences.
4. Binders, if there is something to bind. Cholestyramine is prescription-only and is the cornerstone of Shoemaker's protocol. Activated charcoal is available without one; a 2022 study found it sequestered 99.1% of deoxynivalenol in vitro. Bentonite clay and modified citrus pectin have different binding profiles.
Two safety points about binders. They work in the gut — they prevent reabsorption, they do not pull toxins out of tissue. And they bind indiscriminately: charcoal takes your medications and supplements with it. Take binders away from everything else, and if you take any daily prescription, clear this with a pharmacist before you start rather than after.
5. Support the systems that do the clearing. Chapter 9 lists NAC, liposomal glutathione, selenium, sweating through sauna or hard exercise, and zinc to counteract cadmium displacement.
The honest limits
- No trial has tested remediation, binders, or any mould protocol as a psoriasis intervention. Every number on this page comes from mechanism studies, genetic association studies, or clinical observation.
- The genetic association data is inconsistent across populations, and the book says so.
- The CIRS framework is clinically used and not independently validated, and the book says that too.
- Testing is expensive and easy to over-interpret. The base rate of a positive urine result is close to 100%.
- This is a troubleshooting hypothesis, not a first move. If you have not yet done the light, sleep, diet and weight work, that is where the evidence is stronger and the cost is lower.
- None of this is a reason to change your treatment. Investigating an environmental driver runs alongside whatever your dermatologist has you on, not instead of it.
Where to start
The free Mold & Environmental Burden tool takes about seven minutes and produces the thing this article argues for: a test-first plan that tells you whether to start with an ERMI or a urine panel, and why. It will not sell you a protocol.
If your suspicion is broader than mould, the free Root Cause Profile scores where the pressure is across several domains first — worth doing before you commit to this one. And the free Water & Filter Guide covers the other environmental exposure people most often overlook, starting with the steps that cost nothing.
Chapter 9 of **Heal Psoriasis** has the full mechanism and every citation; Chapter 20 places it correctly, as one of several hidden blockers to check when the rest of the protocol has not worked.
This article is educational information, not medical advice. It does not diagnose, treat, or replace care from a clinician who knows your history. Never start, stop, or change a prescribed medication based on anything you read here — talk to your doctor first. Individual results vary.