Long COVID and CIRS: Could Mould Be Part of It?

Long COVID and CIRS (Chronic Inflammatory Response Syndrome) can look very similar. Both cause fatigue, brain fog, headaches, aches and breathing problems that go on for months. But they are different diagnoses.

Long COVID follows an infection with SARS-CoV-2, the virus that causes COVID-19. CIRS, as Dr Ritchie Shoemaker’s group defines it, follows exposure to biotoxins. Biotoxins are natural poisons made by living things such as moulds. Most often they come from the indoor air of water-damaged buildings.

Only one small study has looked at the two together. It came from Dr Shoemaker’s own group, and nobody else has confirmed its results. Still, it raises a practical question if you have not recovered: am I still being exposed to a damp, mouldy building?

What is long COVID?

The World Health Organization (WHO) calls long COVID post-COVID-19 condition. International experts agreed its definition for adults in a structured consensus process, called a Delphi process [1]. In plain words, long COVID means that:

• you have had a probable or confirmed SARS-CoV-2 infection,
• the condition is usually present 3 months from the start of the infection,
• the symptoms last at least 2 months, and
• no other diagnosis explains them [1].

The symptoms usually make everyday life harder. They can start after you seemed to recover, or carry on straight from the infection. They can come and go, or come back [1].

Well studied The WHO estimates that about 6 in 100 people who get COVID-19 develop long COVID. The rate appears lower now than earlier in the pandemic [2].

More than 200 symptoms have been reported. The most common are [2, 3]:

• fatigue
• muscle or joint pain
• breathlessness
• headache
• problems with thinking, often called “brain fog”
• changes in taste
• sleep problems
• depression and anxiety

Is there a test for long COVID?

No. In 2024 the US National Academies, a body of leading scientists, described long COVID as an infection-associated chronic condition that has lasted at least 3 months. They added two points that matter here [4]:

• No biomarker can confirm long COVID. A biomarker is something you can measure in the body, such as a blood value, that shows an illness. None of the ones available today settles the question.
• Long COVID can exist alongside other illnesses. It is not a diagnosis you get only after everything else has been ruled out.

What causes long COVID?

Preliminary research Nobody knows yet, and there are probably several causes. The WHO and research reviews list these leading ideas [2, 3]:

• virus that stays behind in body tissues
• an immune system that is out of balance
• other viruses waking up again, such as Epstein–Barr virus
• autoimmunity, where the immune system attacks the body’s own tissues
• changes in the gut bacteria (the gut microbiota)
• problems in the small blood vessels

About half of people with long COVID are estimated to meet the criteria for ME/CFS (myalgic encephalomyelitis / chronic fatigue syndrome). Many have post-exertional malaise: their symptoms get worse after physical or mental effort [3].

Mould and water-damaged buildings are not among the causes discussed in these mainstream sources [2, 3]. That does not mean they are irrelevant. It means they have hardly been studied.

Can long COVID be CIRS?

Long COVID is, by definition, linked to a virus. Viruses are not biotoxins. In Dr Shoemaker’s model, a virus does not trigger CIRS by itself (see what triggers CIRS).

So the real question is not whether COVID-19 “is” CIRS. There are two other possibilities:

1. Some people who stay ill after COVID-19 also have CIRS, from an exposure that was there all along.
2. The infection tipped an immune system that was already under strain over the edge.

Expert opinion The second idea is a hypothesis: an idea that has not been tested. A 2024 review written by CIRS practitioners lists long COVID among “potential CIRS conditions” and calls for it to be studied [5]. That is an honest description of where things stand.

What did the Shoemaker study on post-COVID syndrome find?

One small study In 2021, Dr Shoemaker and colleagues published an observational study in Medical Research Archives [6]. Observational means that the researchers measured people. They did not treat them or test a treatment.

Who was studied: 21 people who had tested positive and later negative for COVID-19. They were recruited from doctors’ practices. 14 had not recovered six weeks after the negative test. The study calls them “PCS+” (post-COVID syndrome). 7 had recovered (“PCS−”).

What was measured:

• symptoms
• the visual contrast sensitivity (VCS) test, a vision test of how well you see shades of grey
• GENIE, a commercial blood test of gene activity (which genes are switched on). It was developed for CIRS.

The researchers compared the two groups with each other, with CIRS patients and with healthy controls.

What they found:

	Not recovered (14 people)	Recovered (7 people)
Average number of symptoms	18.2	8.2
Abnormal VCS test	75% (about 3 in 4)	none
Gene pattern the group calls “molecular hypometabolism”	all	none
Gene markers read as exposure to actinobacteria	57% (about 6 in 10)	14% (about 1 in 7)
Gene markers read as exposure to endotoxins	64% (about 2 in 3)	0%

Actinobacteria are bacteria that grow in threads like mould. Endotoxins are parts of the cell walls of certain bacteria. Both are typical of the indoor air of water-damaged buildings. “Molecular hypometabolism” is the group’s own name for a gene-activity pattern; it suggests that cells are running on low power, but that is their interpretation.

What the study did not do:

• No buildings were inspected or sampled. Exposure to water damage was guessed from gene patterns in the blood. It was not measured.
• No treatment was given.

The authors concluded that post-COVID syndrome may occur in people with additional environmental exposures, and that more studies are needed [6].

How much weight can this study bear?

Not much on its own.

• It is small: 14 people compared with 7.
• Nothing in the environment was measured.
• Most of the authors work with CIRS.
• The main test was designed for CIRS. One of the authors works for the company that developed it, and it has not been checked independently for this use.
• The journal is not indexed in PubMed, the main database of medical research.
• Nobody has repeated it. As of October 2026 we found no independent study that has tested a link between long COVID and water-damaged buildings.

The study is a reason to ask the question. It is not an answer to it.

How do long COVID and CIRS compare?

	Long COVID (post-COVID-19 condition)	CIRS (Shoemaker definition)
Starting point	SARS-CoV-2 infection; the condition is usually present 3 months from its start [1]	Exposure to biotoxins, most often the indoor air of water-damaged buildings [7]
Typical symptoms	Fatigue, post-exertional malaise, breathlessness, brain fog, pain, headaches, sleep problems [2, 3]	Fatigue, brain fog, aches, headaches, light sensitivity, breathing and gut symptoms, numbness, thirst, static shocks [7]
How it is diagnosed	Clinical diagnosis; no biomarker confirms it [4]	Symptoms, exposure history, laboratory markers (e.g. MSH, MMP-9, TGF-β1, VIP) and the VCS test [7]
Leading explanations	Virus that persists, immune imbalance, autoimmunity, microclots and others [2, 3]	An ongoing reaction of the innate immune system to biotoxins in people with a genetic susceptibility [7]
Treatment approach	Symptom management, rehabilitation, pacing; research on treatments is limited [2]	End the exposure first, then the stepwise Shoemaker protocol [5, 7]
Strength of evidence	A large international research effort, but still no proven cure [2, 3]	Mostly one research group; few independent trials [5]
Link between the two	One small Shoemaker-group study (21 people) [6]	The same study; not confirmed by anyone else

The innate immune system is the body’s fast first line of defence. Microclots are tiny blood clots.

Why check for water damage if you have not recovered from COVID-19?

Because it costs little to ask. And if there is an exposure, you can do something about it.

Well studied Based on independent research, the WHO concludes that damp and mould in buildings increase the risk of breathing symptoms, respiratory infections and worse asthma. It recommends preventing lasting dampness and microbial growth indoors [8].

Not studied Whether such exposure also helps keep long COVID going is not known. But living or working in a water-damaged building is not good for anyone with ongoing symptoms.

The question is especially worth asking if:

• your symptoms clearly ease when you are away from home or work for several days, and return when you come back
• the building has a history of leaks, condensation, a musty smell or visible mould, or other people there have similar symptoms (see symptoms of water damage)
• you had fatigue, brain fog or recurring sinus problems already before COVID-19, and the infection made them much worse
• you have symptoms that are typical of CIRS but less typical of long COVID, such as strong thirst, frequent urination, static shocks or a metallic taste [7]

None of these proves anything. They are reasons to look more closely, together with a doctor.

What should I do next?

Do not start prescription treatments such as binders on your own. Binders are medicines that bind toxins in the gut. If you are diagnosed with CIRS, the treating doctor decides on medicines and doses.

What is not known?

Being honest about the gaps matters here. Both conditions attract confident claims online.

• Whether CIRS explains any long COVID cases at all. One study of 14 people who had not recovered and 7 who had cannot answer this [6].
• How common water damage is in the homes of people with long COVID. No study has inspected their homes and compared them with the homes of people who recovered.
• Whether CIRS treatment helps people with long COVID. No trial has tested the Shoemaker protocol in long COVID. The 2021 study gave no treatment [6], and the 2024 review calls for this to be studied [5].
• Whether the CIRS markers can tell the two apart. Markers such as MMP-9 and TGF-β1 measure inflammation, not its cause. Even the CIRS consensus statement says that VCS results, laboratory changes or symptoms alone are not enough for a diagnosis [7]. No study has tested how well they separate CIRS from long COVID.

If you have long COVID and someone has suggested CIRS, the most solid ground is this: rule out the usual causes, check for ongoing exposure to a water-damaged building, and judge any diagnosis by proper testing rather than by a symptom list. The site’s founder, Joel Hakala, describes his own path to a diagnosis in his CIRS story.

Remember these

Test yourself: Can you explain why an abnormal VCS test does not prove that someone’s long COVID is CIRS? And why the 2021 study cannot show that mould keeps long COVID going?

What next?

• Read how CIRS is diagnosed.
• Find out whether your symptoms improve away from home.
• Compare CIRS and ME/CFS.

References

1. Soriano JB, Murthy S, Marshall JC, Relan P, Diaz JV; WHO Clinical Case Definition Working Group on Post-COVID-19 Condition. A clinical case definition of post-COVID-19 condition by a Delphi consensus. Lancet Infect Dis. 2022;22(4):e102–e107. PubMed
2. World Health Organization. Post COVID-19 condition (long COVID). Fact sheet, 26 February 2025. Accessed 2 October 2026. WHO
3. Davis HE, McCorkell L, Vogel JM, Topol EJ. Long COVID: major findings, mechanisms and recommendations. Nat Rev Microbiol. 2023;21(3):133–146. PubMed
4. Ely EW, Brown LM, Fineberg HV; National Academies of Sciences, Engineering, and Medicine Committee on Examining the Working Definition for Long Covid. Long Covid defined. N Engl J Med. 2024;391(18):1746–1753. PubMed
5. Dooley M, Vukelic A, Jim L. Chronic inflammatory response syndrome: a review of the evidence of clinical efficacy of treatment. Ann Med Surg (Lond). 2024;86(12):7248–7254. PubMed
6. Shoemaker RC, McMahon SW, Heyman A, Lark D, van der Westhuizen M, Ryan JC. Treatable metabolic and inflammatory abnormalities in Post COVID Syndrome (PCS) define the transcriptomic basis for persistent symptoms: lessons from CIRS. Med Res Arch. 2021;9(7). DOI
7. Shoemaker R, Johnson K, Jim L, et al. Diagnostic process for chronic inflammatory response syndrome (CIRS): a consensus statement report of the Consensus Committee of Surviving Mold. Internal Medicine Review. 2018;4(5):1–47. PDF
8. World Health Organization. WHO guidelines for indoor air quality: dampness and mould. Copenhagen: WHO Regional Office for Europe; 2009. WHO