What Is ‘Brain Fog’ (and When Is It Serious?)

The term “brain fog” can mean many different things, from the afternoon sleepiness you get after a bad night of sleep to the short-term memory loss associated with dementia. Generally speaking, brain fog can consist of memory problems, an inability to focus, or a lack of mental clarity. Although brain fog isn’t a formal medical condition, these symptoms can be a sign that something is going on.

Underlying medical issues that can cause brain fog

There are a number of different medical conditions that can cause brain fog. One major cause can be inflammatory conditions that affect the brain, such as a recent COVID-19 infection or an autoimmune disease.

“When the central nervous system, which includes the brain and spinal cord, gets affected, that can lead to symptoms such as brain fog,” said Carlos Pérez, a neurologist at Baylor College of Medicine.

Metabolic issues, such as a thyroid condition, can also result in brain fog, while certain medications can also be a culprit. Brain fog is especially prevalent in people going through chemotherapy, to the point it has its own name: “chemo brain.”

Another culprit can be hormonal changes, including during pregnancy and menopause. “It’s probably changing hormonal levels that are causing this brain fog,” said Louise McCullough, a neurologist at UTHealth’s McGovern Medical School, noting that this is less concerning because of the self-limiting nature of pregnancy and menopause, which will end eventually (even if it doesn’t quite feel like it).

The timeframe for symptom-onset can vary

The timeframe in which brain fog develops can be useful information for your doctor, as it can help them determine what might be a possible cause. With something like a stroke, the onset will be very fast, developing in a matter of minutes or hours.

In the case of other conditions, such as post-viral complications from a COVID-19 infection, the onset will happen on a scale of days or weeks. For progressive neurological conditions, such as Alzheimer’s or dementia, these symptoms will develop very slowly, over a course of months or years.

When to see a doctor

If your brain fog is starting to impact your quality of life, your ability to do your job, or to carry out your normal daily life, it’s time to see a doctor.

“If it’s progressing, or if it’s very long-lasting, if it’s starting to impair your activities of daily living or your work, you need to see a doctor, because there are a lot of things that could potentially be wrong,” McCullough said.

Another warning sign is if it either comes on very suddenly or if it persists for a while, with no obvious cause. As Perez advises, it’s also important to tell your doctor about any other symptoms you might be experiencing. For example, if the brain fog has a neurological origin, additional symptoms might include weakness, numbness, changes in your vision, or balance issues.

Whatever might be going on, the first step is to see your primary care doctor to get a physical exam and bloodwork done. Depending on your other symptoms and your medical history, they can suggest additional specialists.