If you’ve been struggling with symptoms that don’t have a clear explanation — fatigue that doesn’t go away, brain fog that comes and goes, digestive issues that don’t respond to dietary changes — mold might not be the first thing that comes to mind. Most people think of mold as a problem for old, damp buildings in humid climates. But in our practice in Fort Collins, we see mold illness in people who had no idea they were exposed. We see patients with mold illness symptoms on a daily basis.
Colorado’s dry climate doesn’t make you immune. A slow plumbing leak, a poorly ventilated bathroom, a basement with a history of moisture, or an HVAC system that hasn’t been serviced in years can all create the right conditions for mold to grow indoors — often in places you can’t see. And because mold illness can look like so many other things, it often goes undiagnosed for months or even years.
Here are seven signs that mold illness symptoms might be behind what you’re experiencing:
1. You’re Exhausted — But Nothing Shows Up on Your Labs
This is one of the most common things we hear: “My doctor ran bloodwork and everything came back normal, but I’m exhausted all the time.” Mold illness causes a type of fatigue that isn’t captured by standard thyroid panels or CBC. It’s driven by mycotoxins — the toxic compounds that mold produces — which interfere with how your cells produce energy at a mitochondrial level. You can sleep eight hours and still feel like you haven’t slept at all.
If your fatigue is persistent, doesn’t improve with rest, and has resisted every explanation your doctors have offered, it’s worth considering whether environmental exposure might be part of the picture.
2. Your Brain Doesn’t Feel Like Your Own
Brain fog is one of the most reported — and most frustrating — mold illness symptoms. Patients describe it as thinking through mud: words don’t come when you need them, you walk into a room and forget why, you read the same paragraph three times and can’t retain it. Concentration is unreliable, and the mental sharpness you used to take for granted just isn’t there.
This happens because mycotoxins are lipophilic — they readily cross the blood-brain barrier and directly affect neurological function. Research has documented measurable structural changes in the brains of people with chronic mold exposure. This isn’t a vague wellness complaint; it’s a physiological consequence of ongoing toxin burden.
3. You’ve Become Reactive to Everything
One of the more puzzling patterns in mold illness is the development of new sensitivities — to foods you used to tolerate fine, to fragrances or cleaning products, to wine or leftovers, to medications. Things that never bothered you before now reliably make you feel worse.
This is often a sign that mast cells — the immune cells responsible for triggering inflammatory and allergic responses — are being chronically activated by mycotoxin burden. When mast cells are stuck in overdrive, your threshold for reactivity drops dramatically. This condition, known as Mast Cell Activation Syndrome (MCAS), is closely linked to mold illness and frequently resolves — or significantly improves — when the underlying mold exposure is addressed.
4. You Feel Dizzy or Lightheaded, Especially When You Stand Up
Orthostatic symptoms — dizziness, lightheadedness, or a racing heart when you go from sitting to standing — are more common in mold illness than most people realize. Mycotoxins can disrupt the autonomic nervous system, which is responsible for regulating heart rate, blood pressure, and blood flow when your body changes position.
If you’ve been evaluated for POTS (Postural Orthostatic Tachycardia Syndrome) or dysautonomia and haven’t found a clear cause, mold exposure is one of the factors worth ruling out. We regularly see patients whose orthostatic symptoms improve substantially once their mycotoxin burden is addressed.
5. Your Gut Is a Mess and You Can’t Figure Out Why
Bloating, nausea, unpredictable bowel habits, abdominal discomfort — gut symptoms are among the most common complaints in mold illness, and they’re often the ones patients have been managing unsuccessfully for the longest time. Mycotoxins directly damage the intestinal lining, contributing to increased permeability (commonly called leaky gut) and significant disruption of the gut microbiome.
If you’ve tried elimination diets, probiotics, and gut-healing protocols without lasting improvement, it may be because the underlying driver — ongoing mycotoxin burden — hasn’t been addressed. The gut can’t heal in the presence of a toxin that keeps damaging it.
6. Your Mood and Sleep Have Shifted in Ways That Are Hard to Explain
Anxiety, irritability, depression, and mood instability that seem disconnected from what’s actually happening in your life are another hallmark of mold illness. So is sleep that doesn’t feel restorative — waking up tired, difficulty staying asleep, or vivid and disturbing dreams.
These symptoms have a physiological basis. Mycotoxins disrupt neurological function and affect the production and regulation of neurotransmitters. They also interfere with hormonal signaling — including cortisol and melatonin — which directly affects both mood and sleep architecture. These aren’t psychological symptoms; they’re biological ones.
7. You’ve Seen Multiple Providers and Still Don’t Have Answers
This might be the most telling sign of all. Mold illness affects so many body systems simultaneously that patients often end up bouncing between specialists — a gastroenterologist for the gut symptoms, a neurologist for the brain fog, a cardiologist for the dizziness, a psychiatrist for the mood changes — each of whom sees only their piece of the picture and finds nothing definitive.
If you have symptoms across multiple systems, have had extensive workups that came back unremarkable, and have been told that stress or anxiety might be the culprit — mold illness is a legitimate diagnostic consideration that deserves investigation.
But I Live in Colorado — Isn’t Mold a Humid Climate Problem?
It’s a reasonable assumption, but it doesn’t hold up in practice. Mold doesn’t need a humid climate — it needs a moisture source. In Colorado homes, those sources are common: HVAC systems that haven’t been properly maintained, bathrooms without adequate ventilation, crawl spaces, basements, and any area that has experienced water damage — even years ago. Mold can grow behind walls and under flooring without ever being visible, and it can persist long after the original moisture problem has been fixed.
In our Fort Collins practice, we see mold illness in people who live in perfectly ordinary Colorado homes and have never had a visible mold problem. Environmental exposure history is one of the first things we ask about when a patient presents with unexplained multi-system symptoms.
Why Does Mold Make Some People Sick and Not Others?
Genetics play a significant role. About one in four people carry gene variants — specifically in the HLA-DR immune system genes — that impair the body’s ability to recognize and clear mycotoxins. In these individuals, toxins don’t get efficiently eliminated. They accumulate, recirculate, and drive a self-perpetuating inflammatory response that can persist long after the original exposure has ended.
This is why two people can share the same home and have completely different experiences. It’s also why mold illness can continue — or even worsen — after someone has moved out of a moldy environment, if the underlying toxin burden hasn’t been addressed.
What to Do If You Recognize These Signs
The first step is getting a thorough evaluation — one that takes your environmental history seriously and goes beyond standard lab panels. Mold illness requires specialized testing: mycotoxin urine testing, genetic susceptibility markers, and innate immune system assessment are not part of a routine workup, but they can reveal patterns that explain symptoms that have otherwise gone unaddressed.
At Rocky Mountain Natural Medicine, Dr. Sarah Kashdan has specific experience evaluating and treating mold illness and environmental exposures. If you’ve been dealing with unexplained symptoms and want a comprehensive assessment, we’d be glad to talk through what that process looks like.
You can also read more about our approach on our Mold Toxicity Treatment page, or schedule a complimentary 15-minute consultation to discuss your history and whether this line of evaluation makes sense for you.