as high school boys, Jesse Einhorn and his friends had many heated discussions.

In the candlelit, arid chamber of the Einhorn family’s sauna in Bar Harbor, they would tackle the tough issues at hand – philosophy, school, girls. Sometimes, Jesse’s father, David, would come in and tell stories of growing up in the ’60s or of the civil rights movement. Other times he would listen and give advice.

The conversation flowed in the hot, dry air, punctuated by the occasional burst of steam as Jesse or David threw a ladle of water onto the sauna rocks. When it got too hot, the guys would go outside and jump into the ocean or roll around in the snow, then they’d head back to the sauna to take away the chill.

“In high school and to this day, it’s sort of a fun thing to do,” said Jesse Einhorn, now 19 and a sophomore at Haverford College in Haverford, Pa. “We go in and it gets hot and then we run down to the ocean. We go down in the middle of winter and jump in the ocean.”

On Mount Desert Island, it’s torture to jump into the ocean in the summer, even when the water heats up to a balmy 50 degrees. So taking a dip in Frenchman Bay isn’t the most appealing thought in January. But winter is the time to get the full sauna experience, contrasting extreme heat and cold, whether it’s in the form of a chilly shower, a frozen lake, a frigid sea or a fresh coat of snow.

“You always have to have the contrast from the heat to the cold,” said

Melita Brecher, 55, who lives a street over from the Einhorns in Bar Harbor. “That moment when you immerse yourself in the water is the hardest part, but when you get out, your body is warm. If you don’t cool off at all, you’re going to sweat for the next hour.”

The hot-and-cold ritual got its start more than 2,000 years ago in Finland, where sauna is pronounced SOW-nah, as opposed to the English SAW-na. In its most basic form, a sauna is a wooden room with benches, ventilation holes, and a stove on which rocks are heated to create a hybrid of a dry-heat bath and a steam bath. Here, it’s a way to relax and ease sore muscles. In Finland, the sauna is a way to cleanse the skin, but it also is ceremonial.

“Sauna is not only for cleansing – it’s also a meditative experience,” said Brecher, who grew up in Finland and moved to Bar Harbor with her husband, Stewart, about 18 years ago. “You go into the sauna and your voice gets softer, your breathing is different. It’s a time when your mind really relaxes.”

Inside the sauna, it’s too hot to breathe deeply or speak loudly. The temperature should range between 167 and 212 degrees F, according to “The International Handbook of Finnish Sauna” by Allan Konya and Alewyn Burger. Though this sounds extreme (212 degrees is the temperature at which water boils) people can stand dry heat at temperatures much higher than moist heat. Periodically, water is thrown onto the rocks to create steam, which encourages perspiration to purge the pores of impurities. In Finnish, both the process of throwing the water and the steam itself are called loyly, pronounced LUR-lou.

In the United States, people sometimes cleanse themselves with a dry brush. In Finland, it is part of the ritual to prepare a vihta (VEE-tah), a switch of supple birch branches and leaves tied together with another branch – no string allowed. People then take turns beating the vihta gently on each other’s backs to increase circulation.

“Of course, you don’t beat yourself until you’re purple. It should be a pleasurable experience,” Brecher said. “From my childhood, I really remember the smell of the birch leaves on the floor. They give wonderful smells.”

Jesse Einhorn and his friends sometimes throw a little eucalyptus oil in the water bucket for scent, but for them, the sauna experience is less about procedure and more about reflection and camaraderie.

“We’re tapping into something very old and very good,” said Nick Katona, 20, of Bar Harbor.

“That’s what imparts the seriousness to the sauna,” added James Gilmore of Somesville. It’s like a ritual.”

David Einhorn compared the young men’s “ritual” to “Dead Poets Society” meetings, but they disagreed, saying their sauna sessions were more like something out of MTV.

“You talk about very important stuff,” Gilmore, 21, said. “It’s kind of like ‘The Real World’ only you’re in a sauna.”

Either way, the elder Einhorn was impressed by “the fact that they were doing this on Friday and Saturday night and not out drinking.”

“It’s just a very healthy activity,” David Einhorn said. “I’ve always loved saunas, even before I lived here. It’s very cleansing for the mind and body and soul.”

His sauna, a free-standing outdoor model that seats five comfortably and up to 10 in a pinch, was built by students at College of the Atlantic who used to live on the property. Over the years, Einhorn added to the sauna, but retained some of its funky features, such as the sun-shaped window in the door. The original model was heated by a wood stove, but Einhorn switched over to electric heat awhile back.

“My father, knowing it would be a linchpin of adolescent social life on the island, was wise to switch over to electric,” Jesse Einhorn said. “Now all you do is flip a switch.”

Brecher, an artist, built her pine and cedar sauna from a kit so she’d have somewhere to warm up after working all day in her unheated studio. It seats two comfortably and is kept in a room off her kitchen. It has an electric stove and takes a little more than an hour to heat up.

“Of course, wherever Finns go, they always take their sauna with them,” Brecher said. “If you can financially, you always have a sauna.”

In Finland, saunas aren’t a luxury – they’re a way of life. There, a sauna is as common as a shower is in the United States.

“Every apartment built in Finland has a sauna,” Brecher said. “Even studios have them, in connection with a shower and a bathroom. No matter how small your apartment is, you still squeeze in a sauna. … If you buy a piece of land, the first thing you do is build a sauna and then comes the house.”

As a girl in Finland, Brecher had access to two saunas – one, a public sauna in Helsinki near her family’s home, the other, a smoke sauna beside a lake at her family’s country house.

“I remember just chopping wood for a whole day just to do that. That’s the drawback with a smoke sauna,” Brecher said.

A smoke sauna takes nearly all day to heat up. To heat it, wood is burned in a stove that has no chimney, so smoke fills the room and soot stains the inside walls black. Once the sauna is hot enough, the door is opened and the room is aired out.

“You walk out and your butt is all black and you’re leaning on the walls, so your back is all black, so we joke that you come out more dirty than you went in,” Brecher said.

Although they are sooty and somewhat dangerous, the smoke saunas are prized among Finns.

“People in Finland love the smoke saunas,” Brecher said. “If you have a smoke sauna, it’s a good thing. You try to keep it alive as long as possible.”

When her family’s sauna burned down years ago, it wasn’t a tragedy, though. Brecher’s husband, who is an architect, rebuilt it with boards from an old farmhouse.

“Now we have a really nice one,” Brecher said.

Even though the old sauna is gone, her family’s traditions have continued.

“We have this ritual in Finland. After the sauna we make a bonfire by the lake, fry some hot dogs on the flame, fry some crepes. That’s the tradition we have in our family. It’s really wonderful. You’re all bundled up after the sauna, enjoying the silence of the lake.”

Because people sweat so profusely in a sauna, it is customary to have beverages and a salty meal afterward.

“When you come out of the sauna the traditional thing is to have a beer or a soft drink because you need to get liquid into your system,” Brecher said. “Some people have heard that sauna is something that helps you lose weight, and that’s not true. You lose fluid, but you have to replenish it.”

Novice sauna users need to be careful not to get dehydrated. They should start off with a lower sauna temperature, keep plenty of water on hand outside the sauna, and avoid overdoing it with the loyly – a little steam is a good thing, but too much can be unbearable and unhealthy.

Even experienced sauna users should limit their time in the heat to 10-minute intervals, followed by a cooling-off period.

Used correctly, the sauna can be a therapeutic, healthy way to clean the body, clear the head and rejuvenate the muscles.

Plus, as the smooth-skinned Brecher has found, the sauna has some benefits that go beyond cleansing.

“It’s the sauna that keeps me young,” she said.