The Mysterious Microbe In Your Gut: What To Know About Blastocystis Hominis

Just the word “parasite” is enough to make most people uncomfortable. But parasites are surprisingly common, and they’re often misunderstood. 

Blastocystis hominis is a great example. I see this parasite all the time on stool tests, and it’s the subject of a lot of debate and confusion. 

Is blastocystis hominis a problem? Could it be the cause of your symptoms? Does it need to be treated, or is it a red herring? 

While the answer to a lot of these questions is “it depends”, I’m going to break down what you need to know to have more clarity on what role this parasite may play in your overall gut health. 

What Is Blastocystis Hominis? 

Blastocystis hominis, often shortened to b hominis or “blasto”, is a parasite that can live in the human gastrointestinal tract. This parasite is very common, with up to 15% of individuals in developed countries carrying it in their digestive tracts. (1) 

B hominis was originally thought to be a type of harmless yeast, but once researchers were able to sequence the RNA they discovered it was in fact a protozoan parasite (a single-celled organism that has adapted to live in the cells or tissues of a host). (2) 

Researchers have also now discovered at least 17 different subtypes of b hominis. 

Where scientists and practitioners are still unclear or in disagreement is about whether or not blastocystis hominis causes harm. It’s also unclear whether different blastocystis subtypes may affect us differently. 

Some experts (particularly in the conventional medicine field) believe b hominis is a normal, harmless commensal organism that can simply be ignored. Others link blasto to digestive symptoms and imbalances, and believe it needs to be eradicated in order to heal someone’s gut. 

As with most debates of this nature, the answer likely lies somewhere between the two, as we’ll explore in much more detail below. 

How Is Blastocystis Hominis Transmitted? 

Blastocystis hominis, like most parasites, is spread through fecal-oral transmission. This can happen as a result of drinking contaminated water, eating unwashed fruits and vegetables or contaminated food, or coming into contact with unclean surfaces. 

LISTEN: Parasite Deep Dive: Symptoms, Labs, Cleanses + Treatments For This Gut Health Problem (+ Emotional Parasites That Damage Your Health!) | Dr. Will Cole 

A home water filter is a great way to ensure your water is not contaminated, and good, standard hygiene practices (like proper handwashing), as well as carefully cleaning produce, can help to cut down on additional risk. However, even when taking these precautions, it’s not uncommon to contract a parasitic infection. 

B Hominis Symptoms and Associations 

Some people carry blastocystis hominis without ever knowing it or experiencing symptoms. For others, it’s been associated with symptoms including: (3) 

• Abdominal pain or cramping 
• Bloating and gas
• Diarrhea, constipation, or alternating diarrhea and constipation
• Nausea
• Loss of appetite or anorexia 
• Fatigue 
• Skin rashes
• Intense itching 
• Iron deficiency anemia
• Food intolerances or reactivity

Keep in mind that these can also all be symptoms of many different kinds of health conditions, or of a gut microbiome imbalance (dysbiosis) more broadly. Blasto is definitely not the first place I look when I see bloating and fatigue. 

For example, a bacterial overgrowth or the presence of other problematic microbes may actually be responsible for the symptoms that blasto is also associated with. This is why it’s so important to look at the gut microbiome as a whole (and stepping back even further, to look at the whole person). When we focus too narrowly on eradicating one questionable organism, we can end up further disrupting the balance of the gut ecosystem. 

With that said, there are a number of links between blastocystis hominis and certain health patterns and conditions: 

• Irritable Bowel Syndrome (IBS): Some studies have shown a higher prevalence of blastocystis in people with IBS. (4) 
• Autoimmunity: Case studies have shown symptom improvement and remission in Hashimoto’s thyroiditis and ulcerative colitis with the eradication of b hominis. (5, 6) 
• Chronic skin disorders: Blastocystis has been suggested as a potential contributing factor to some cases of chronic urticaria (hives) and other skin conditions. (7) 
• Mood and behavior: Some research suggests that blastocystis may affect mood, stress resilience, and anxiety, likely by influencing tryptophan metabolism. (8) 

There are some factors that may make an individual more susceptible to harm from a parasite like blastocystis hominis. These may include an already imbalanced gut microbiome and chronic or severe stress. 

Testing For Blastocystis Hominis

If you haven’t already, the first thing to do when you suspect blastocystis hominis or another parasitic infection is to run lab tests with a trusted practitioner. 

The standard testing method for parasites is a DNA PCR (polymerase chain reaction) stool test, which is very sensitive and can detect tiny fragments of DNA from organisms like blastocystis hominis within a stool sample. 

This testing method is used in conventional medicine settings as well as integrative or functional medicine settings. 

In functional medicine, we generally recommend a more comprehensive stool analysis. This type of test uses the same or similar technology but screens for more things including bacterial overgrowths and yeast or fungal infections, and gives a greater overall picture of the gut microbiome. 

Remember that if this parasite shows up on the stool test, all it tells you is that this organism has been detected in your gastrointestinal tract. These tests can’t tell you whether or not b hominis is responsible for your symptoms or whether it’s causing any problems. 

That’s why it’s important to take a holistic view of gut health and not jump to blaming blasto for symptoms just because you see it on your stool test. You want to consider it, but not in isolation. 

Does Blastocystis Hominis Require Treatment? 

So, does blastocystis hominis need to be treated? This is one of those questions that requires us to ask more questions. 

The first and most important question to ask is: are you experiencing symptoms? If you see b hominis on a stool test but you’re not feeling unwell, there is likely no reason to treat it. It may be there as part of your diverse and healthy microbiome, and in fact you could in theory create a problem by disrupting it. 

If you see blasto on your stool test and you’re experiencing symptoms that seem connected to it, then it may require treatment. 

Some studies have shown that treating blastocystis hominis directly does tend to improve symptoms, including in children with abdominal pain and individuals with ulcerative colitis and chronic hives. (9, 10, 11)

However, in most cases we still want to take a more global and holistic view of the entire gut microbiome rather than zooming in specifically on this one parasite. 

READ MORE: How To Heal Your Gut: A Functional Medicine Guide To Restoring Microbiome Health 

It’s important to rule out other causes, and look at other potential pathogens, imbalances, and overall inflammation. And when we focus on rebalancing the gut terrain rather than just trying to kill this one microbe, a blastocystis infection will often essentially resolve itself. 

Can B Hominis Actually Be Helpful? 

While it may be counterintuitive, some studies have shown that blastocystis is actually more common in people with strong, diverse, healthy microbiomes, suggesting that in some contexts it may actually support gut balance rather than disrupting it. This may be in part due to its ability to stimulate the production of mucus in the gut. (1)

This can feel confusing, but as a different example, think of a high FODMAP food like broccoli. For someone who has an overall healthy and balanced gut microbiome, this food is likely to be beneficial, as it feeds healthy bacteria. But for someone with a bacterial overgrowth or imbalance, broccoli can feed the overgrown bacteria, contributing to a further imbalance and symptoms. 

While blasto doesn’t work in exactly the same way, I use this example to illustrate how a variable can differently affect two different people depending on the overall state of their gut microbiomes. 

Treatment Options For Blastocystis Hominis 

In conventional medicine, the standard treatment for b hominis is the antibiotic metronidazole (Flagyl). But research has shown that blasto is often resistant to metronidazole, or that the infection recurs. (12, 13) 

And, of course, antibiotics can wreak further havoc on the gut microbiome. Given all of this, I would always recommend trying a more holistic approach first. 

There are a lot of great herbal antimicrobials, but even these shouldn’t be thrown indiscriminately at the situation. 

Make sure that you’re supporting a healthy and resilient gut microbiome that can handle antimicrobial treatment by doing the following: 

• Remove sugar and processed foods from your diet, at minimum. These can both fuel parasites and disrupt gut microbial balance overall. Many people also feel best when removing gluten and dairy. 
• Eat an anti-inflammatory diet rich in whole foods
• Eliminate alcohol 
• Support a healthy gut with probiotics and gut repairing nutrients as needed (especially if you have or suspect leaky gut)
  • Probiotics, particularly saccharomyces boulardii (which is actually a beneficial yeast), have been shown to help clear out b hominis (1) 
• Incorporate a regular stress management practice into your routine 

From there, you may want to introduce antimicrobial herbs and supplements, such as: 

• Berberine, or berberine containing herbs such as barberry 
• Oregano (1)  
• Wormwood
• Black walnut
• Pomegranate husk 
• Olive leaf extract
• Curcumin or turmeric root extract (14)

There are also several healthy foods with anti-parasitic properties which you can work into your diet. These include: 

• Garlic
• Ginger
• Pumpkin seeds
• Turmeric 

Again, if you’re asymptomatic, b hominis likely doesn’t require treatment. 

Focus On the Bigger Picture

In summary, blastocystis hominis can in some cases cause symptoms, but it’s essential to take a holistic view of the situation. Essentially blasto is a lab finding, and whether or not it’s harmful depends on several individual factors. 

In most cases, the best approach is to focus on supporting overall gut health rather than zeroing in on this one organism. 

For more personalized support with your gut health, book a consultation with our telehealth functional medicine center. 

As one of the first functional medicine telehealth clinics in the world, we provide webcam health consultations for people around the globe.

Sources

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• Zierdt, C. H. (1991). Blastocystis hominis–past and future. Clinical microbiology reviews, 4(1), 61-79.
• Kaya, S., Cetin, E. S., Aridogan, B. C., Arikan, S., & Demirci, M. (2007). Pathogenicity of Blastocystis hominis, a clinical reevaluation. Turkiye parazitol derg, 31(3), 184-7.
• Maghsood, A. H., Kayedimajd, S., Motavallihaghi, S., Abedian, R., Kordi, S., Davoodi, L., … & Soleymani, E. (2024). Irritable Bowel Syndrome Associated with Blastocystis hominis or Without Relationship to It? A Case–Control Study and Minireview. Acta Parasitologica, 69(1), 639-647.
• Rajič, B., Arapović, J., Raguž, K., Bošković, M., Babić, S. M., & Maslać, S. (2015). Eradication of Blastocystis hominis prevents the development of symptomatic Hashimoto’s thyroiditis: a case report. The Journal of Infection in Developing Countries, 9(07), 788-791.
• Jeddy, T. A., & Farrington, G. H. (1991). Blastocystis hominis complicating ulcerative colitis. Journal of the Royal Society of Medicine, 84(10), 623-623.
• Bahrami, F., Babaei, E., Badirzadeh, A., Riabi, T. R., & Abdoli, A. (2020). Blastocystis, urticaria, and skin disorders: review of the current evidences. European Journal of Clinical Microbiology & Infectious Diseases, 39(6), 1027-1042.
• Leonardi, S. S., & Tan, K. S. W. (2024). Blastocystis: View from atop the gut–brain iceberg. Trends in Parasitology, 40(1), 1-4.
• Toro Monjaraz, E. M., Vichido Luna, M. A., Montijo Barrios, E., Cervantes Bustamante, R., Zárate Mondragón, F., Huante Anaya, A., … & Ramirez Mayans, J. A. (2018). Blastocystis hominis and chronic abdominal pain in children: is there an association between them?. Journal of tropical pediatrics, 64(4), 279-283.
• Tai, W. P., Hu, P. J., Wu, J., & Lin, X. C. (2011). Six ulcerative colitis patients with refractory symptoms co-infective with Blastocystis hominis in China. Parasitology Research, 108(5), 1207-1210.
• Tuzer, C., Yegit, O. O., Sonmez, N., Ertek, B., Demirpek, U., Demir, S., … & Colakoglu, B. (2025). The eradication of Blastocystis spp. subtype 3 improves the course of chronic spontaneous urticaria. International Archives of Allergy and Immunology.
• Haresh, K., Suresh, K., Anuar, A. K., & Saminathan, S. (1999). Isolate resistance of Blastocystis hominis to metronidazole. Tropical Medicine & International Health, 4(4), 274-277.
• Nigro, L., Larocca, L., Massarelli, L., Patamia, I., Minniti, S., Palermo, F., & Cacopardo, B. (2003). A placebo-controlled treatment trial of Blastocystis hominis infection with metronidazole. Journal of travel medicine, 10(2), 128-130.
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