Why Can’t I Think Straight on a Hot Day?

Constantly active and churning out heat, the brain is already fighting to stay cool—so on a really warm day, it can easily crash and burn.

The brain is a demanding organ: its 90 billion electrically active brain cells are fussy about temperature, and they start to misfire and suffer damage if body temperature rises by just 3–4ºF.

Your prefrontal cortex, or “thinking” region near the front of your brain, is particularly vulnerable—that’s why heat stroke causes wooziness, muddled thinking, and confusion. On a hot day, your reaction times won’t drop much and you’ll be able to remember simple things such as a phone number, but anything more complicated than that—like paying close attention, driving, or solving a tricky problem—becomes progressively more difficult as your prefrontal cortex buckles in the heat.

Symptoms of heat exhaustion can involve dizziness, fainting, vomiting, and even seizures. Young children’s brains are extra heat-sensitive.

If you live in warmer climes, then your body will usually be better adapted to get rid of excess heat. The body’s go-to climate control methods are flushing the skin, where the blood rushes to the surface to release heat, and sweating, which cools you down by drawing heat from the body as the sweat evaporates.

It’s not just our brains that dislike the heat; our muscles perform more poorly, too—it’s better to leave hard, physical work for when the temperature is 68°F (20°C) or below.