Pachuta, 19, now realizes that the vision issues she experienced were the result of migraines, triggered by the heat.

Since then, heat waves have become more frequent and lengthy worldwide, because of climate change. An estimated 39 million Americans live with migraine, according to the American Migraine Foundation. Half of those with migraine report the weather as one of their headache triggers, according to Elizabeth Loder, chief of the Brigham and Women’s Hospital Headache Division.

Here’s what to know about heat headaches and how to avoid them.

Does heat really cause headaches?

Heat can be a major factor, experts agreed, though the onset of a headache is often a mix of compounding environmental factors.

High temperatures are frequently accompanied by changes in barometric pressure, direct sun exposure and humidity, and these environment changes can trigger a headache for those who have migraine.

“Migraine brain does not like variability,” said Jessica Ailani, neurologist and director of the Headache Center at MedStar Georgetown. “It wants you to sleep at the same time, eat the same thing. So big shifts in temperature and weather don’t do well with migraine.”

Experts are unsure of the precise mechanism by which heat can trigger a headache, though heat can lead to processes that are known to cause headache. Extreme dehydration can cause your brain to shrink and pull on the blood vessels lining the brain, which can lead to physical pain, Loder said.

In extreme cases, heat can affect the function of brain neurons, according to Mayo Clinic neurologist Narayan Kissoon. Altered cell function leads to an increase in activity in the pain centers of the brain, he said.

What’s the difference between a headache and a migraine?

A headache is a common symptom of many illnesses, said Loder, whereas migraine is a neurological disorder that causes headaches.

“It’s like the difference between sneezing (possibly an allergy) and a cold (which is a specific viral disease),” Cherubino Di Lorenzo, the neurology chair at Sapienza University of Rome, said in an email.

People diagnosed with migraine experience headaches because of a variety of factors, including stress, dehydration, a lack of sleep — and, yes, heat, experts said. Women suffer from migraine more than men. Migraine usually comes with other symptoms, such as nausea, fatigue, dizziness and hypersensitivity to light or sound.

Pachuta finds relief from a heat-induced migraine by lying in a dark room with her eyes closed until the pain behind her eyes subsides. She can catch a migraine attack early if a mild headache is accompanied by a general feeling of being “off.”

But heat is unlikely to trigger a headache in those who aren’t typically afflicted with them, Loder said.

In these cases, a headache induced by high temperatures can be the sign of a more severe related heat-illness, such as heat exhaustion or heat stroke, Loder said. It’s important to recognize these symptoms early, rehydrate and find a place to cool down.

Dehydration can certainly worsen your body’s ability to deal with the heat, but it’s not necessarily the cause of heat-induced headache, experts agreed.

Extreme heat can lead to electrolyte imbalance, as the body loses sodium through sweating, meaning it’s important to replenish yourself with electrolytes as well as water.

“Dehydration is closely tied to electrolyte imbalances as water follows salt,” Kissoon said. “With loss of salt, the body is less able to hold on to water.”

Nevertheless, heat headaches can occur even when someone is well hydrated.

Patrick Cortesi, 55, is a landscaper for his local school district in Bloomington, Ill. Because his job requires him to be outside 40 hours per week, Cortesi wears sun-protective gear, drinks plenty of water, and takes breaks in the air conditioning throughout the warmer days of the year. Even so, Cortesi suffers multiple headaches during the week in a region known for its seasonally muggy conditions, which can create corn sweat.

“It’s not just dehydration,” Ailani said. “You have to take better care of yourself anytime the heat index gets to this point … you can’t just drink this away.”

What can you do to alleviate symptoms?

Don’t just brush it off, experts said.

A heat-induced headache, especially if you don’t suffer from migraine, is a sign that things could get worse. Get out of the heat and try to cool yourself down with a cold drink or an ice pack. Seek air conditioning indoors and take advantage of cooling centers during a heat wave.

Drink water and electrolyte drinks to help your body replenish itself. Add electrolytes to your water by sprinkling in some salt or lemon juice, Ailani said.

Then you can use the strategies that typically help you manage a headache, Loder said, such as lying in a dark room with your eyes closed.

Avoid known food triggers and cut down on alcohol, which can contribute to dehydration, Kissoon said. Sugary drinks can also lead to dehydration, Di Lorenzo said.

Another seemingly obvious suggestion? Avoid outdoor workouts during high temperatures.

“It seems a trivial advice, but almost all the cases reported in the literature of heat stroke headache have happened in those who did not follow this rule of common sense,” Di Lorenzo said.

If you do need to be outside, sunglasses can be a helpful preventive measure, he added.

There are several tried-and-true over-the-counter medications for headache, such as aspirin and Tylenol. Doctors can also prescribe triptans, which work by binding to serotonin receptors and preventing the release of substances that stimulate nerve activity, Loder said.

Migraine treatments recently approved by the Food and Drug Administration include CGRP antagonists, which target the molecule that plays a role in headaches. Lasmiditan, which functions similarly to triptans, can be safer for migraine patients with a history of vascular disease, Kissoon said.

Additionally, preventive treatments such as CGRP monoclonal antibodies block the action of CGRP and are taken by a person with migraine regardless of whether they have a headache.

“We recommend that a person with migraine who has six or more days per month of any sort of headache be on a preventive medication to reduce the days that they have a headache,” Kissoon said.

For those who are struggling with headache, it’s important to touch base with your health-care provider.

“It’s not a hopeless thing,” Ailani said. “There’s lots of treatments to help get through these hard months.”