8 Potential Causes of Brain Fog

We have all experienced days or weeks where we don’t feel as sharp. We may forget things more, have trouble with recall, lack mental clarity, and can’t concentrate or focus at work. When it's bad, you can feel like a zombie just trying to cut through the fog to function. This experience is often referred to as brain fog.  


young man suffering from brain fog


Brain fog is not a medical condition itself but is often a symptom of a medical condition. It is a type of mental fatigue or cognitive dysfunction that can make studying, working, or completing daily tasks challenging. It can be very troubling and negatively affect mood as well. According to Sabrina Romanoff, PsyD, “ultimately, brain fog can impact the way you feel about yourself. Individuals often do not feel like themselves as the loss of mental sharpness feels foreign to them.”


For some, brain fog can last much longer than a couple of weeks and become a permanent fixture – if not addressed. The first step in addressing brain fog is determining what it is a symptom of. Determining the cause of the brain fog will target the area in your life or health that needs to be addressed so you can start feeling like yourself again. Here are eight potential causes of brain fog:


  1. Lack of Sleep


One of the most common reasons you may not be feeling as mentally sharp is because you didn’t get a good night's sleep. Research has found that just one night of inadequate sleep can result in brain fog the next day. These effects are compounded when disrupted sleep continues night after night as it does with insomnia.    


lack of sleep


If you haven’t been sleeping as well, despite laying on your comfortable buckwheat pillow, it could be the cause of your brain fog. You need about 8 hours of sleep a night for optimal cognitive functioning. So when you have trouble sleeping, whether that be from jet lag or stress, try taking a natural sleep aid to straighten out your circadian rhythm and get your sleep cycle back on track.


  1. Medication


If you have been taking a new prescription or over-the-counter drug, it could be the reason you are experiencing brain fog. Medication is a common cause of brain fog and mental fatigue – in fact, you may see it listed as a potential side effect if you read the small print. In many cases, your doctor can remedy this by lowering your dosage or prescribing an alternative drug.



One of the most notorious brain-fog-causing drugs is chemotherapy. It’s been dubbed “chemo brain” and is partially due to the intense nature of the drug. Those undergoing chemotherapy often have trouble remembering details, multi-tasking, finishing tasks, or focusing. The good news is that once a person stops the medication, their cognitive function returns.  


  1. Medical Conditions


Brain fog can be triggered by some cancers as well. If the cancer has affected the brain, it can affect its function and result in varying degrees of brain fog. Studies have also found that medical conditions involving inflammation, glucose levels, and fatigue can impact mental function. For example, brain fog is a symptom of chronic fatigue syndrome and fibromyalgia. Those with fibromyalgia often experience a level of fogginess every day, which is aptly called “fibrofog.”


medical conditions


Multiple Sclerosis (MS) also can cause brain fog. This disease impacts the central nervous system and alters the way the brain communicates with the body. Roughly 50% of those with MS have trouble with memory, attention, language, or planning. Additional brain-fog-inducing conditions include migraine, hypothyroidism, depression, anemia, diabetes, arthritis, and lupus.


  1. Stress


Stress is a significant contributor to brain fog. When you are under a lot of stress, whether dealing with a sick family member or a big project at work, you may feel like your brain can’t keep up. Chronic stress wreaks havoc on our minds and body. It triggers depression, increases blood pressure, weakens the immune system, and causes mental fatigue. When you are stressed, it is like your brain is running on a treadmill. It goes and goes, and becomes more and more tired with time. When your brain is exhausted, it is tough to reason, focus or think.




An effective way to reduce stress is to practice meditation. Spending just 10 to 15 minutes on a meditation pillow each morning will calm your mind and have a lasting effect on your stress levels. When you reduce the stress, you will also reduce brain fog.



  1. Diet


A diet lacking nutrients, sufficient calories, and variety could cause brain fog. Your brain needs calories to function. It’s the fuel that allows you to concentrate, solve problems, think critically, communicate and process information. These brain tasks are calorie-intensive, so when you aren’t eating enough, your brain can’t operate at its full potential resulting in brain fog. Your brain (and body) like the calories from carbohydrates and use these for energy, so when a diet cuts out carbs, it can take some time for your brain to adjust. This commonly happens with the keto diet and is known as “keto brain.” When a person is eating carbohydrates, the brain uses these for fuel, but when the person stops, it doesn’t get the same energy until it starts to use other sources like protein and fat. This period is usually temporary and remedied with time.




Additionally, a diet lacking vitamin B12 can reduce brain function. Vitamin B12 supports brain function, and a 2021 review revealed that a deficiency in the vitamin could cause brain fog. If you have food allergies or sensitivities yet continue to eat these foods, it can cause brain fog. Common food sensitivities include peanuts, dairy, and aspartame. By removing the trigger food, you could improve symptoms.


  1. Hormonal Changes


Hormonal changes resulting from menstruation, menopause, or pregnancy can cause brain fog. A study in 2018 found that hormonal changes trigger it. During pregnancy, hormones estrogen and progesterone increase significantly, which can cause short-term cognitive impairment. This, too, has another name and is often called “baby brain” or “pregnancy brain."

hormonal changes


Often hormones will balance out gradually after the baby is born, although it can last a couple of years until a woman fully feels like herself again. During menopause, the drop in estrogen levels can cause poor concentration and cloudy thinking. With menopause, hormone therapy may help.


  1. Seasonal Allergies


When you have an allergic reaction, as you do with seasonal allergies, histamines are released. Histamines are chemicals in the body that are produced when you encounter an allergen. It is an inflammatory response that can also cause you to feel fuzzy-headed.


seasonal allergies


Often allergies can also disrupt sleep, making brain fog worse, and causing a downward spiral. The good news is that an over-the-counter allergy med can often reduce symptoms and allow you to get better sleep.


  1. Dehydration


Dehydration can cause brain fog and, when prolonged, can even cause brain cells to shrink and increase the risk of dementia. Every single function in our brain and body requires water.Check out our article about how much water should you drink if you want to learn more about the important of staying hydrated.




We are made up of over 70% water, and when we are lacking, it has a number of adverse side effects. Just a 2% loss in water can cause sleep issues, anxiety, brain fog, headaches, and feelings of depression.


When you are exercising or in hot weather, be sure you are consistently hydrating. The average adult loses up to two liters a day through waste, breathing, and sweating, and if you aren’t topping up your fluids, you could feel the effects of brain fog. The good news is that in just 20 minutes of re-hydrating, the symptoms will be reversed, and your brain fog will dissipate.


With so many potential brain fog causes, it isn’t always easy to determine the reason (unless it is super apparent, like pregnancy). As a result, no single test can determine the cause of brain fog. To determine the cause of your brain fog, a doctor will have to do a complete exam and often request information on your diet, activity levels, medications, and mental health. Additionally, if you are experiencing any other symptoms like weight gain or hair loss, you should tell your doctor. 


In some cases, a blood test will be able to reveal a cause such as inflammatory diseases, infections, irregular glucose levels, and poor liver function. Other diagnostic tools may include an x-ray, MRI, or CT scan.


In addition to discovering the root cause of your brain fog, there are some things you can do that may help clear the fog. Meditation and regular exercise have been found to increase mental alertness, energy, and brainpower. An intense workout where you break a sweat may also break the mental clouds! You should also ensure you eat a balanced diet rich in healthy fats, whole grains, fruits, and vegetables and drink plenty of water. As a result, your body and brain will get the nutrients it needs to make you feel better.


Brain fog can be very frustrating and make daily tasks a challenge. When the lifestyle adjustments don’t help, or you are experiencing additional symptoms, you should speak with your doctor.


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