As a light, hot breeze blew through her living room and her gray hair, Donata Grillo, a 75-year-old cancer survivor with a pacemaker and serious sight problems, sat next to her balcony, a damp sponge on her lap.

It was all she had to keep cool this week as temperatures topped nearly 106 degrees Fahrenheit, or 41 Celsius, in her native Rome. She does not own any air conditioning or fans, or even a functioning refrigerator, in her two-bedroom apartment in a public housing complex on the city’s periphery, next to a hospital and highway.

“It is the feeling of straining pasta all day long,” Ms. Grillo said, twirling her hands to mimic the pouring of boiling water from a pot. A visit from a social worker was about the only contact she’d had in days, the heat having shunted her inside.

“Don’t go anywhere, it’s too hot and dangerous for you,” Carlotta Antonelli, 28, who works with the Roman Catholic charity Caritas, told her during her rounds on Wednesday.

The successive heat waves that have scorched Italy and the rest of southern Europe over the past week have forced those who can afford it to seek shelter in air-conditioned homes and offices or at seaside retreats. But for many seniors, heat has become the new Covid. The searing temperatures have settled over the continent like another indiscriminate plague, reinforcing the isolation of many older people and the threats to their health, and pushing governments and social services to take extraordinary steps to try to protect them.

“These days, they are even more alone,” Ms. Antonelli said, as she drove her car through two large, low-income suburban areas where her charity routinely assists dozens of residents. She visits Ms. Grillo once a week to help her with daily chores and assist with medical appointments and legal problems.

As temperatures rise, the threat to Europe’s elderly is now widespread, with southern European nations being joined by others as far north as Belgium in putting heat plans in place, many aimed at safeguarding older populations.

For Italy, the extreme heat has forged a pincer with the country’s most pressing demographic trend — an aging population — to present an especially acute crisis. About 24 percent of Italians are over 65, making it the oldest country in Europe, and over 4 million of them live alone.

Last year, Italy was exposed to extreme temperatures longer than most other European countries, enduring three major heat waves. Almost 30 percent of the 61,000 people estimated to have died last summer from extreme heat in Europe were Italians, with age playing a significant factor. The number of Italians over 80 is now about 4.5 million, almost double the number of 20 years ago.

“Older people with pre-existing illnesses are more vulnerable,” Andrea Ungar, the president of Italy’s Society of Gerontology and Geriatrics, said in a phone interview. “But poverty and isolation also play a crucial role.”

Europe’s hottest summer on record, in 2003, left more than 70,000 people dead, by some estimates, and since then Italy has only grown older. It has struggled to adapt.

“It was hot even before 2003 in Italy, and we already had a large population of elderly people, but not like nowadays,” said Francesca De Donato, the epidemiologist whose department gathers meteorological and demographic data from across the country to issue the daily bulletins for heat-related health warnings, tailored by city.

“The quota of people at risk has been constantly growing here,” Ms. De Donato noted.

After 2003, Italy became one of the first countries in Europe to put in place a national plan to mitigate the impact of extreme heat, based on the guidelines from the World Health Organization.

The measures include an alert system to warn people to modify their behavior to safeguard their health. Authorities have recently urged hospitals and general practitioners to pay special attention to the most vulnerable people, and they have set up a free phone number where people can seek advice or help for heat-related problems.

Days like Wednesday, when the heat wave peaked, are marked in red on the daily bulletin that Italy’s Health Ministry issues to warn residents. Television channels periodically broadcast the ministry’s guidelines, advising people to stay indoors during the hottest hours; to wear light clothes and sunscreen; to drink lots of water, eat fresh fruits and avoid coffee and alcoholic beverages; and to be particularly careful when going outside.

France, which has been largely spared the heat waves this summer, has a heat tax to fund programs to protect its most vulnerable people, including regular telephone check-ins or in-person visits during heat waves. It also has a heat alert system, or “plan canicule,” that successive governments have activated every summer since 2003.

The hottest summer on record killed 15,000 in France, the majority of them older people, living alone in city apartments or retirement homes with no air conditioning. Last summer, when successive heat waves hit the country, more than 2,800 French people died, some 80 percent over the age of 75, according to the French public health authority.

As rising temperatures creep north to countries less accustomed to them, Belgium has set up a three-step heat plan, based on regular monitoring of temperature and ozone levels. In Brussels, seniors and those who feel isolated or vulnerable can register over the phone with municipal authorities, who will check on them regularly as soon as temperatures climb above 84 Fahrenheit. The social workers distribute fluids and check living conditions. Still, Belgium’s excess mortality rate rose to 5.7 percent during the hottest months last summer, the highest in 20 years.

In Greece, the country’s archaeological sites will be closed between noon and 5.30 p.m. through Sunday, when temperatures are set to reach 111 in Athens. The Ministry for Civil Protection has said that all government services are “in a state of increased readiness to deal with the consequences of high temperatures.”

There, as elsewhere, the advice from authorities amounts to a simple imperative: Stay home. That has placed a special onus on governments and social workers to make sure isolation itself does not become a hazard.

In Rome, a team of regional health professionals checks in via phone calls with the most vulnerable people, mostly the elderly and infirm, on days flagged orange or red for the most severe heat.

While the hardships and isolation of the most vulnerable in many ways echo the fight against Covid, the pandemic also left some good practices in place, including visiting and treating people in their homes, health officials said. A 2022 law, passed by the government of the former prime minister, Mario Draghi, pushed for better coordination between health services and telemedicine. Italian health authorities are working to have one digital platform with updated patient information that visiting nurses, doctors, emergency services and hospitals can access.

“Covid has shifted the mentality on some services, and that has helped a lot,” said Andrea Barbara, a public health official who oversees services for about a million residents in Rome. “We do more telemedicine, we are increasingly moving equipment — and not the patients — but it takes time.”

Even those who don’t need medical aid, assistance remains crucial and, for many vulnerable people, associations like Caritas are still the most reliable weekly help. Ms. Antonelli, the social worker, carried two cases of slightly fizzy water up two flights of stairs for Francesca Azzarita, a 91-year-old who lives alone with nothing to cool herself but a piece of cardboard to use as a fan.

“Carlotta, when you are not coming, I feel like I am lost,” Ms. Azzarita said in a thick Neapolitan accent that she hasn’t lost despite living in Rome for almost 50 years.

Ms. Azzarita, a little girl when World War II broke out, never learned to read and write and has worked all her life, first in the countryside around Naples and later as a cleaner in Rome, where she moved after separating from her husband.

Now her morning starts with coffee and a painkiller for her aching legs. She usually cooks for herself alone, but these days, she doesn’t turn on the stove because it is too hot and she rarely leaves her home, especially after she fell on the sidewalk last week.

“Temperatures have changed since I was a girl,” she said. “I don’t need to watch the TV to know that the rain was normal and the sun was normal, and now it is not.”

She then glanced at Ms. Antonelli, still panting from the stairs. “How would I do without her help?” she said.

Niki Kitsantonis contributed reporting from Athens, Catherine Porter from Paris and Monica Pronczuk from Brussels.