Ever notice a drop in energy after a few hours in the sun? Or that you start to feel irritable or just meh? It’s likely because the heat kickstarts a few important processes in your body, including signaling you when it’s time to head inside to cool down. To help understand these mood shifts, LaTasha Seliby Perkins, MD, family physician and an assistant professor at Georgetown University School of Medicine, breaks down what’s going on inside your body when it’s hot outside. Plus, she shares how to stay safe in the heat.
theSkimm: Why does being out in the sun make me tired and cranky?
Perkins: “Your body's doing everything it can to keep you cool or keep your core temperature around 98.6 [degrees Fahrenheit]. It's sweating, it's limiting your body's function in other areas, … [such as] digesting food, … [and it’s] trying to keep the blood flow to places where it should be.
“Your skin is your major source for cooling you down. When you’re laying in the sun, most of your blood flow is going to go toward your skin. If there are patches of skin that are sunburned, that skin isn’t going to function at its full capacity to cool you down because it's also working to heal itself. Some of the blood flow that generally goes to your brain will [also] go to your skin in an effort to cool you down. Which means your cognitive functioning isn't as high as it would be if your temperature was normal.
“Because your body's doing all these functions, it [can] be literally draining. That's why you're getting tired. And that's also the reason why, when the temperatures are extremely high, you're asked to stay cool [and] stay out of direct sun. [When] your body is no longer able to maintain that core temperature, that's what can cause people to get heat exhaustion or heat stroke. [With] heat exhaustion, you literally have no energy to do [things you may want to do]. All you want to do is rest. [If you’re getting tired], it’s a sign that you need to hydrate and it's a sign that you need to get out of the heat.
“Dehydration [and] your temperature being too high [can make you cranky]. If you’re dehydrated or you’ve been in the sun too long, your heart rate goes up significantly in an effort to keep you cool. If you have a history of anxiety, that increase in heart rate [can] also make you more anxious.
“Temperature, humidity, and activity make a difference. [Humidity] makes it so that that ability to cool down by just sweating doesn't really work — there's no dry air to dry the wetness off. So, if you're going from an air-conditioned car to an air-conditioned building, you're fine. But [with] exercise and prolonged time outside in the heat, you really need to be mindful of the temperature and listen to your body. [Take the heat] in moderation: 30 to 45 minutes if you're sitting in the sun, and probably 15 minutes [to] 20 minute bouts where you're actually stopping and taking a break.”
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