What Causes Brain Fog? 12 Common Triggers
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Does your brain feel like it’s running at half-speed? We’ve all been down the brain-fog road at one point or another. But why does it happen? We dug into the science to give you a full rundown of what can cause brain fog.
Sometimes brain fog causes are pretty obvious—like when you spent most of the night tossing, turning, and making a (very long) mental to-do list instead of actually sleeping. Other times the source of a hazy mind is a mystery.
“Brain fog is like an unorganized computer,” says Michele Leno, Ph.D., a licensed psychologist at DLM Psychological Services in Michigan and the host of “Mind Matters With Dr. Michele” in Detroit. “You know the information is there, but retrieving it takes several minutes, or more.”
And those foggy feelings are all too common, especially among women. Some research estimates 44% to 62% of women in perimenopause (which can last for five years or longer, usually starting in your 40s) report having brain fog. But it’s not exclusive to middle age. Brain fog befalls younger women (and yes, men), too.
So, we know what brain fog is, and we know we’re probably going to experience a bout of it at some point, if we haven’t already. But what causes brain fog? In short: lots of things. Let’s dig into the top causes of brain fog to figure out what you need to know.
Mental health issues
“Anxiety, depression, and high stress can affect cognitive functions,” Leno says. “Persistent emotional distress overloads the brain and its ability to function properly.”
Multiple parts of the brain are involved in mental health. One of these is the amygdala, which Leno calls “the emotional brain.” It’s involved with learning and memory and helps us process information and emotions. Plus, it regulates anxiety and fear responses.
When we feel overwhelmed by anxiety, stress, or other mental health issues, it’s as if an internal dam breaks and “floods” the amygdala. Research has found amygdala activity is higher in people with depression. This is often associated with confusion, poor recall, and difficulty focusing.
Imbalances in neurotransmitters and fluctuations in hormones are tied to depression, anxiety, and other mental-health disorders. Insomnia or disrupted sleep are also regular issues in people struggling with their mental health — also often making our minds feel muddy.
Hormonal imbalances
Women commonly experience brain fog at times when their hormones fluctuate: during their menstrual cycle, during pregnancy and postpartum (hello, baby brain), and the menopause transition.
Sex hormones like estrogen, progesterone, and testosterone are involved in brain function. Estrogen, especially, is linked to cognitive processing. Estrogen receptors exist in areas of the brain that regulate cognition and mood. Plus, estrogen has anti-inflammatory and other protective qualities for the brain and assists in the growth and repair of brain cells.
Cortisol, one of the stress hormones, also has a lot to do with those foggy feelings. When we’re stressed about work, our kids, or just general busy-ness (and, seriously, who isn’t), cortisol levels can rise as part of the sympathetic nervous system’s response to that stress. When we’re chronically stressed out, cortisol keeps our brains and bodies on high alert. High cortisol is also disruptive to sleep.
“When cortisol is peaking, it can impact memory and focus,” says Brianna Paruolo, LCMHC, a licensed clinical mental health counselor at On Par Therapy in New York City, who works mostly with high-achieving Gen Z and young Millennial women. “Our brain is going to kick into high gear, into hyperarousal, and it’s harder to search for those words, those memory callbacks, or do things you want to do.”
Not producing enough thyroid hormones (hypothyroidism) or too much (hyperthyroidism) affects how the body uses energy, making fatigue a common problem already. Similarly, an imbalance of the hormone can also lead to problems with memory and concentration.
Perhaps not surprisingly, fatigue and forgetfulness are the most common brain fog symptoms in people with a thyroid disorder. People receiving thyroid replacement treatment also often report experiencing brain fog, with many saying they experienced it before treatment.
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Nutritional deficiencies
What we eat fuels our minds and our bodies. A deficiency in certain nutrients can affect how our brains work and increase the chances of brain fog, as well as depression and anxiety.
VItamin B12
Even mildly low levels of vitamin B12 can affect how well our brains work. Research has found lower vitamin B12 levels are tied to reduced cognitive performance, including poorer memory and slower thinking.
Vitamin D
Don’t skip that sunshine. Vitamin D is thought to have neuroprotective benefits for brain cells against inflammation and oxidative stress. The vitamin might also influence the hypothalamic–pituitary–adrenal (HPA) axis, which regulates stress hormones like cortisol.
Iron
Iron helps with the production of red blood cells, which move oxygen to the brain. Not enough of it can equal fatigue and a fog-filled noggin.
Magnesium
Magnesium also has protective properties for the brain and boosts neuronal plasticity—the mental flexibility that supports learning and memory. A magnesium deficiency can also result in neuroinflammation.
Zinc
Zinc is linked to memory, learning, and mental sharpness. Not enough of it can lead to classic brain fog symptoms. But there can be too much of a good thing when it comes to zinc: an excess can actually harm brain cells and disrupt nerve signaling.
Omega-3 fatty acids
You’ve probably heard the claims about fish oil pills and brain function, right? Those are omega-3 fatty acids at work. The three main omega-3’s are ALA (found mostly in plant foods), DHA, and EPA (found mostly in fish and seafood). Omega-3’s have been found to boost learning, enhance memory, and decrease inflammation.
| Nutrient | RDA for Women | RDA for Men | RDA for Pregnancy | RDA for Breastfeeding |
|---|---|---|---|---|
| Vitamin B12 | 2.4 mcg | 2.4 mcg | 2.6 mcg | 2.8 mcg |
| Vitamin D | 15 mcg (600 IU) | 15 mcg (600 IU) | 15 mcg (600 IU) | 15 mcg (600 IU) |
| Iron |
18 mcg (until age 50) |
8 mcg | 27 mcg | 9 mcg |
| Magnesium | 320 mg | 420 mg | 350–360 mg | 310–320 mg |
| Zinc | 8 mg | 11 mg | 11 mg | 12 mg |
| Omega-3 Fatty Acids | at least 250 to 500 mg combined EPA and DHA 1.1 mg ALA |
at least 250 to 500 mg combined EPA and DHA |
at least 250 to 500 mg combined EPA and DHA |
at least 250 to 500 mg combined EPA and DHA |
Lack of sleep
We’ve all experienced the brain haze that follows a night of awful sleep, so no surprise here: Sleep is good for the brain. Lack of sleep is not.
Poor sleep affects how well our brains work in a multitude of ways. Memory, learning, reaction time, alertness, attention, decision-making are all negatively impacted when we don’t catch enough high-quality zzz’s.
Unfortunately, plenty of things can mess with our sleep. Alcohol and caffeine consumption are biggies. Elevated cortisol levels can make it harder to wind down in the evening and sleep well. Declines in estrogen and progesterone during the menopause transition are also factors.
Autoimmune disorders
Brain fog is a familiar experience for many people with autoimmune disorders, including fibromyalgia, multiple sclerosis (MS), lupus, celiac disease, chronic pain, and rheumatoid arthritis.
There are more than 80 different autoimmune disorders and they don’t all work the same in the body. Generally speaking, though, autoimmune disorders are caused when the immune system attacks healthy tissue by mistake. Some research indicates inflammation caused by this overactive immune response may contribute to brain fog.
Long COVID
Brain fog—particularly problems with memory, executive function, and attention—have emerged as one of the “most frequent persistent” symptoms of long COVID.
Research has found a few potential reasons for COVID-related brain fog, including a disruption of the blood-brain barrier, causing changes to the brain structure. Another likely factor is chronic systemic inflammation throughout the body.
Lyme disease
Brain fog is a top symptom in people who’ve contracted Lyme disease, along with joint pain and severe fatigue. And, unfortunately, Lyme disease is common, with an estimated 476,000 people being diagnosed with and treated for Lyme each year. Using advanced neuroimaging, like PET scans, researchers have found inflammation and structural abnormalities in the brains in patients with Lyme as compared to patients who don’t.
Infection or illness
Besides COVID-19 and Lyme, other illnesses and infections can lead to cognitive impairment. Many of these can trigger inflammation—a familiar culprit of brain fog.
Any brain-related infection or illness, such as encephalitis or meningitis, can spur brain fog, memory problems, and other cognitive issues (in addition to other symptoms like fever and severe headache). Epstein-Barr virus— the precursor to mononucleosis—impacts the blood brain barrier, and can cause a sense of fogginess in addition to extreme fatigue.
Migraines
It makes sense: When your head hurts so much that it’s hard to see, you’re probably not going to be thinking clearly.
But brain fog and memory slips aren’t exclusively tied to the acute pain of a migraine—you might notice their onset before a migraine attack or that they linger for a while afterward. One possible explanation is that the movement of electrical pulses and blood from the back of the brain to the front prior to a migraine (called cortical depression) slows down cognition.
Medications
Plenty of medications can make people feel foggy, including antihistamines, antidepressants, anti-anxiety meds, sleep aids, pain medications, and chemotherapy treatment. Oftentimes, it’s because the meds disrupt signals between hormones or neurotransmitters and brain cells.
But the medication may not always be directly to blame. “Sometimes there’s a snowball effect,” Leno says. “A medication or health condition may not directly cause brain fog, but it may cause another problem that affects the brain.”
One example? Insomnia, sleep disturbances, and excessive drowsiness are common side effects of medications (you’ve heard them listed in the commercials, no doubt). If sleep gets messed up, it has a ripple effect on our memory, concentration, and alertness.
Chronic fatigue syndrome
Chronic fatigue syndrome (CFS) is notoriously difficult to diagnose, as symptoms can come and go and fluctuate in their severity. In fact, up to 90% of people who have CFS have not been officially diagnosed.
Beyond physical fatigue that doesn’t improve after resting, most people with CFS have some problems with memory and thinking. So, what causes brain fog and fatigue in CFS? It’s not yet clear, but it’s possibly a combination of multiple triggers related to the immune system, stress, infection, and genetic predisposition.
Aging
Yes, as we get older, we lose some of the mental sharpness we once had in our youth. And there are plenty of potential age-related causes.
Memory slips and confusion can be early indicators of dementia, with the risk increasing the older we get. But brain fog may also result from lifestyle factors, like sleep, diet, and exercise.
Age-related cognitive issues could also be tied to medications we’re taking or an underlying health condition we have (and the older we get, the more likely we’ll be taking at least one medication for something). The blood-brain barrier weakens over time, so drugs or toxins that were once kept out of the brain now might be seeping in.
The bottom line
Brain fog is a general sense of haze and malaise in the control room upstairs, and there are many potential causes. These include physical health conditions, mental health conditions, lifestyle factors, and hormonal imbalances. Knowing exactly what’s causing your brain fog is the key to finding the right treatment and alleviating your symptoms.
Key takeaways
- Brain fog has many potential causes, including a variety of physical and mental health conditions, simple things like a lack of sleep, and lifestyle factors like what you eat.
- Vitamin deficiencies, excess stress, and poor sleep can negatively impact brain function.
- Inflammation is associated with brain fog from long COVID, migraine, autoimmune disorders, and other illnesses and infections.
- Many common medications are also linked to brain fog.
- Working with a trusted medical professional to identify the cause of your brain fog is key to easing the symptoms.
Frequently Asked Questions
For sure. Anxiety and brain fog are often in a loop, with one making the other worse. The chemical and hormonal imbalances, hypervigilance, and rumination of anxiety—plus the poor sleep that often accompanies it—overwhelm the brain and make it harder to think clearly.
Definitely. Chronic stress can trigger a combo of high cortisol, disrupted sleep, and an overtaxed brain, leaving us feeling hazy and spacy.
The brain regulates cognition and mood, and water makes up 75% of the brain. When you’re dehydrated, your brain cells don’t work as well, which can affect clear thinking, focus, and short-term memory.
Yes. Cognitive impairment is very common in people with depression. Imbalances in brain chemicals and neurotransmitters can lead to brain fog, as can certain antidepressants.
Quite a few nutrients are linked to brain fog, if you don’t get enough of them. The big ones are zinc, vitamin B12, omega-3 fatty acids, iron, vitamin D, and magnesium.
There are lots of ways to try to prevent or lessen your brain fog, including getting plenty of sleep, managing stress, and cutting back on alcohol, added sugar, and ultra-processed foods. But even if you tackle the root cause of your brain fog, there’s no guarantee you will “cure” brain fog forever. It’s possible you might experience it again for a different reason.
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