a man with clouds over his head to represent brain fog

7 Surprising Reasons Your Brain Is So Sluggish

Plus fixes for lack of concentration, memory issues, and mental muddyness.

Lacking the concentration to get through a full article on your phone or struggling to remember what you ate for lunch yesterday can be disarming. Before you go down a dark Google rabbit hole, know this: There are plenty of causes of brain fog—and plenty of fixes.

The good news: If you haven’t hit the age when you can file for Social Security, its unlikely that your brain lapses are elated to degenerative brain disease like dementia or Alzheimer’s, says Jennifer Frontera, M.D., a professor of neurology at NYU Langone Grossman School of Medicine. Nor are chronic cognitive lapses likely to be triggered by structural brain problems like a stroke or brain tumor.

Cognitive blips are more likely caused by more commonplace problems like stress, a lack of sleep, or illness.

To better understand the causes of lack of concentration, memory lapses, and forgetfulness—and when you should be concerned by them—here’s a breakdown of some of the most common causes of brain fog and what to do about them.

What Is Brain Fog?

While there’s no clinical definition for brain fog, many describe it as difficulty concentrating, retrieving memories, learning new tasks, or retaining new information, says Frontera.

Causes of Brain Fog

If you’re feeling forgetful, absent-minded, or straight-up out of it, don’t assume the worst.

Instead, start by cataloging your lifestyle habits, Frontera suggests. You may be able to spot changes that are causing mental fatigue.

If tracking your symptoms and habits doesn’t shine a light on a cause, make an appointment to speak with your doctor. He or she can ask questions and run tests that can help identify the problem.

Here are a few things they may be on the lookout for.


Brain fog can linger after an initial Covid infection, reoccur, or crop up anew in the weeks following your diagnosis.

How can a respiratory virus mess with your mind? “We wish we knew,” says Frontera.

“Researchers are questioning whether it may be a combination of mood disorders (1), structural injuries (2) such as tiny brain hemorrhages resulting from the virus, hypoxic damage at the time of acute COVID, metabolic disorders (such as hypothyroidism (3), vitamin deficiency, etc.), neurodegenerative processes, or some combination of these causes and others, but more data is required.”

One thing that’s becoming apparent: The sicker you get with the virus, the more likely you are to experience lingering symptoms including cognitive disruption in the weeks and months that follow your initial illness, according to Frontera.

Of course, there’s also the stress and mental anguish involved in temporary isolation—that loopiness that comes on when you deviate from your regularly scheduled routine and step out of society for a while. Anecdotally, that can also mess with your mental clarity in addition to long COVID itself.


Lack of Sleep

Whether you’re getting too few hours of sleep or poor quality rest, it can come back to bite you during daylight hours.

“Because sleep is the time when the brain cleans up cellular waste, it’s integral to performing at your cognitive best,” says Frontera.

To keep your brain in top shape, you need a minimum of 7 hours of sleep per night, according to the Centers for Disease Control.

If the clock says you’re getting enough sleep but you feel mentally foggy during the day, ask your partner if you snore or your breathing pauses at night. If so, see a sleep doctor and get evaluated for obstructive sleep apnea, a common sleep disorder.

Marked by breathing disruptions that can compromise your oxygen intake while you snooze, sleep apnea can tank the quality of your sleep and lead to trouble concentrating, making decisions, or remembering things (4).

B12 Shortage

Dietary insufficiencies may be one of the most surprising causes of brain fog.

Your physician may run blood work to detect deficiencies in vitamins such as B12, which has been linked to impaired cognition and memory.

B12 is found in foods including meat, dairy, fortified cereals, eggs, and poultry, but some people do not eat enough of those foods to get adequate B12. Vegans and vegetarians are especially at risk.

Some studies have found that vitamin B12 deficiency may lead to depression, memory loss, and problems with cognition (5).

If blood tests reveal that you are B12 deficient, supplements or B12 shots can correct your levels.


Thyroid Issues

When your thyroid underperforms—as is the case among those diagnosed with hypothyroidism—you’re bound to feel off-kilter.

“Low levels of thyroid hormones may cause issues with focus, memory, and even communicating,” says Richard Foxx, M.D., a physician who specializes in hormone replacement therapy, wellness, and sports medicine. Other red-flag symptoms of a thyroid deficiency: weight gain, fatigue, dry skin, and headaches.

Testing your blood for the chemical released by the pituitary gland—thyroid-stimulating hormone or TSH—can confirm whether your thyroid is functioning properly and whether treatment is needed.

If you do have hypothyroidism, daily doses of synthetic thyroid hormone can usually solve for most symptoms, including brain fog.

Low Testosterone

Men’s testosterone levels naturally dip with age, says Foxx. Because testosterone facilitates certain pathways in the brain, this gradual hormonal change can contribute to depressive symptoms, interfere with your sleep, and cause mental fogginess, he explains.

The only way to know for sure if your testosterone levels are low is to get a blood test. Your doctor can order one, or you can order an at-home test from Hone.

Could You Have Low T?


Syphilis may sound like ye olde disease of Tudor kings, but diagnoses are on the rise. In 2021, over 2,600 cases of congenital syphilis were reported, according to the CDC, and men made up the bulk of the cases (6).

While the sexually transmitted bacterial infection is known to manifest in the form of sores, syphilis can migrate to the brain when left untreated.

Neurosyphilis, as is called when it reaches the brain, is associated with irritability and depression as well as certain cognitive challenges—difficulty concentrating or general confusion, both of which can be categorized as brain fog (7).

A simple blood test can confirm a case, and antibiotic treatment can improve—or in some instances even reverse—symptoms.

Does Brain Fog Go Away On Its Own?

In some cases, brain fog will slither away as subtly as it struck—particularly if you address what Frontera refers to as “housekeeping issues,” that is, improving your lifestyle to address the poor sleep, deficiencies, or depression.

How Do You Get Rid of Brain Fog?

Relief and recovery from brain fog begin with a call to your primary care physician, who can run basic blood tests and determine whether a neurologist referral is needed.

“If the thought crosses your mind that you’re concerned about your cognition, it’s best to air on the side of caution and be evaluated,” says Frontera.

Once a diagnosis is made, therapy, pharmaceuticals, and lifestyle interventions may be available to alleviate your symptoms. But really, it all depends on what lies beneath your brain fog—and how quickly you address it.

The Bottom Line

Illness, lack of sleep, mood disorders and hormone deficiencies can all lead to brain fog. If you can’t put your finger on any lifestyle changes that may be responsible for fogginess, see your physician as soon as you notice a change in your memory or mental clarity.