Maybe you're frustrated that you forgot to pack yourself a breakfast for the third time this week, or you're spacing out while catching up with a friend over coffee, or finding it just straight-up impossible to concentrate on work. We've all felt a bit off at least once in our lives, as if we're looking at the world through frosted glass. The internet loves to call that feeling "brain fog," and it's usually (thankfully) temporary. But what is it? Brain fog isn't really a medical term, which makes it that much harder to pin down what's going on when it's not so temporary — and it turns out there's a lot that could be going on. In general, the symptoms of brain fog include forgetfulness, slowed thinking, and trouble concentrating. The good news is that the most common causes of that foggy feeling aren't a sign of something scary going on. These causes include not getting enough sleep, waiting too long between meals, and stress (of course). In these cases, the fog tends to clear after you address the underlying cause, meaning your quick thinking will return once you finally get your eight hours of sleep or call off your juice cleanse. In other words, the vast majority of the time, the healthy habits you already know you should be incorporating into your day are also the ones that will help your brain keep clicking. But when the feeling sticks around even after your sleeping patterns return to normal, something else may be causing it. One common culprit is your hormones, especially estrogen. Indeed, people frequently report "brain fog" as part of the transition into menopause. There's also some evidence to suggest hormonal changes may be responsible for the slight memory impairment some people experience during pregnancy. Then there's your thyroid hormones, which help regulate your energy levels among many other things. So if you have a thyroid issue (an underactive one in particular), you may notice fatigue and a general feeling of sluggishness, physically and mentally. Mental fogginess is also a common symptom of many mental disorders, including depression and bipolar disorder, as well as a side effect of many medications used to treat those illnesses. On top of that, these conditions often interfere with other factors that influence your mental clarity, including your ability to get good sleep, keep up with physical activity, and maintain balanced nutrition. So you could be fighting an even more difficult battle to keep the fogginess at bay. There are other causes, of course. For instance, cancer patients may experience "chemo brain" as a side effect of chemotherapy. Brain fog is also a hallmark among those with chronic fatigue syndrome. And as you age — especially when you reach 65 or so — it becomes more likely that mental fog could be the early stages of actual cognitive impairment due to a neurological disease, such as Alzheimer's. But please don't panic — if you're nowhere near your "golden years," and you don't think your symptoms are actively getting worse, that's probably not something you need to be too concerned about. Basically, this all comes down to the fact that what we know as "brain fog" is actually a bunch of different issues with a bunch of different root causes. If you're concerned about your sudden inability to locate your glasses and you don't have one of these other conditions, your first steps should be getting enough sleep, exercise, and nutrition-packed food. Finding an effective way to deal with stress is also key here, so it may be time to give meditation or yoga a try. But if you're well-rested, totally chilled out, and still having problems, a check-in with your doctor is probably in order. She'll be able to help you pinpoint the underlying cause and cut through that fog for good.