Tourists are missing on Greek islands in the heat. Here’s how to stay safe.

Here are some tips for staying safe in the heat, particularly if you are hiking alone.

How did Albert Calibet and the other tourists go missing?

Calibet went missing on the island of Amorgos on Tuesday, according to the municipality. He is a seasoned hiker and left on what should have been a four-hour hike to meet a friend, his brother Oliver told Fox 11 on Thursday — but he never arrived.

The deputy mayor of the island told a Greek news website that Calibet had walked the trail before and said that the heat may have played a role in his disappearance.

On Sunday, a 74-year-old Dutch tourist went missing after going hiking alone on the island of Samos, Reuters news agency reports; his wife reported him missing that afternoon.

The same day, the body of British doctor and TV host Mosley, 67, was discovered four days after he went missing while walking alone on the island of Symi. The path he was walking was littered with rocks and no shelter as the heat rose to 37 degrees Celsius (98.6 degrees Fahrenheit), according to the Associated Press.

His wife said in a statement that Mosley “did an incredible climb, took the wrong route and collapsed where he couldn’t be easily seen by the extensive search team.”

How hot can the Greek islands get?

Greek islands are usually several degrees cooler than the mainland, according to Nikolaos Pappas, a professor of tourism development and crisis management at the University of Sunderland in England.

But temperatures can still get very high — Amorgos saw temperatures of over 94 degrees Fahrenheit on Tuesday, the day Calibet went missing.

On Tuesday, the country’s meteorological service warned of high temperatures across the country until Friday.

Temperatures rose to above 104 degrees Fahrenheit in much of central and southern Greece on Thursday, prompting authorities to close archaeological sites in Athens and prompting warnings of wildfires, the Associated Press reported.

Last year, Greece and southeast Europe experienced one of the worst heat waves on record.

How can you stay safe in the heat?

The human body is “actually quite well equipped to deal with heat in general,” but in extreme heat, the body sweats more, which can dehydrate the body, George Havenith, a professor of environmental physiology and ergonomics at England’s Loughborough University, said in a phone interview Friday.

Advice for dealing with high temperatures includes staying hydrated, wearing light clothing and sunscreen, and avoiding exercise or even going outside in the peak hours — in Greece, that would be between 11 a.m. and 4 p.m., according to Havenith. If you don’t have access to air conditioning, consider using a fan and perhaps wetting your T-shirt to provide extra cooling.

“Alcohol is better left alone,” he said — not just because of its impact on the body and the possibility of becoming dehydrated more easily, but also “because the decisions you’re going to make might not be the best decisions.”

It’s also important to remember that it can take the body time to acclimatize to a new environment: If you’re in a warmer temperature for even an hour and a half per day over the course of two weeks, the body’s sweat rate and production tend to get higher, according to Havenith, but inactivity affects the rate at which this happens.

There are also some groups who should be more careful in extreme heat, including anyone taking medication: Blood pressure medication, for example, affects the kidneys and can make you more vulnerable to the effects of high temperatures.

Older people may be particularly vulnerable as they often have preexisting conditions and take medications that can make them more vulnerable, he said. “There’s very few people above 70 that take no medication. And that medication can affect your temperature regulation,” Havenith said.

Children and pregnant individuals may also need to take more care.

What should you do if you get heat stroke?

If you or someone you’re traveling with begins to fall ill in the heat, the first stage is heat exhaustion.

“You have a very high heart rate, you’re sweating like crazy,” Havenith said. “And that usually is covered very well by getting people out of the sun and putting them in a cold area, spraying them with water, sprinkling them, a cool bath, a cool shower, to bring the temperature down” — although you need to be more careful if the person has a heart condition, for example.

The next, and more dangerous, stage is heat stroke.

“Cognitively they start to respond less or they can’t walk straight, they can’t tell you who they are, where they are, etc. So once you see those symptoms, it’s really very serious and you need to respond very quickly.”

He says to cool the person with water or put them under a shower and loosen any clothing before calling an ambulance: “The quicker you can get the temperature down, the more chances of survival people have.”

What other safety measures should you consider?

Pappas, the University of Sunderland professor, says tourists should prepare for the reality of the destinations they’re traveling and not make assumptions.

If you’re not used to the local conditions “because you live somewhere else, you need to ask the locals, you need to ask the experts — your travel agent, maybe, [or] if you do not have a travel agent, the reception of the hotel you live — on whether it is a good idea to do something or not.”

A hike or walk that may be manageable in your hometown may be much more difficult on a normal summer day in Greece, he warned — and all the more so during a heat wave.

He notes that in Greece and some other Mediterranean destinations, authorities may close attractions during the warmest part of the day to help protect tourists, as happened in Athens this week.

For hikers, he advises following designated trails and traveling with others so they can help raise the alarm if something goes wrong. He warns against undertaking activities you wouldn’t do at home, such as hiking in extreme temperatures.

As The Washington Post has previously reported, there are other things you can do to keep safe if you are hiking alone: Check the forecast often and heed any weather warnings, carry essentials and let others know your route and when you expect to return.