The reasons are well documented. First, touching, human or otherwise, raises levels of oxytocin in the body, creating feelings of contentment. And, of course, the comfort that an unconditionally loving animal provides in bed is a emotional balm, especially for the depressed, lonely or anxious.  “Animals are uncomplicated and keep us in the present tense,” said Mark Doty, the author of a memoir called “Dog Years,” which chronicles the death of a lover. “When Wally could barely move, I saw him lifting his hand to reach over and pet Beau, our young retriever, who was curled up next to him. He couldn’t even feed himself, but he had the strength and will to give comfort to a dog at his side. It was remarkable.”  It’s no surprise that pet owners like Mr. Doty seem unconcerned about the study published earlier this month by the C.D.C., in which two California doctors warn that allowing pets to sleep in the bed can be dangerous and can spread zoonoses (pronounced zoh-AN-ee-sees), pathogens that go from animals to people. According to Bruno B. Chomel, a professor at the University of California at Davis, and Ben Sun of the California Department of Public Health, the risks are rare, but real. They cite instances of fleas from cats transmitting bubonic plague. Cat scratch fever is a danger, too, they say, as are various forms of meningitis, Pasturella pneumonia and other infections.  “We know these are just the tip of the iceberg,” said Dr. Chomel, who said he has owned dogs and cats, but has never allowed them in the bedroom. “There are risks and precautions to take. But we aren’t telling people not to be close to their pets.”  That’s a good thing, because kicking pets out of bed isn’t likely to be an option for many people. First of all, it’s difficult to retrain animals once they have established a routine. Erica Lehrer and Richard Goldman of Houston learned that when they tried to keep their three cats out of the bedroom after installing an expensive black carpet.  “They staged a protest: cried all night, pounded with their cat paws on the door,” said Ms. Lehrer, 52, a writer. After three sleepless nights, she said: “They won and moved back in. We bought a really good vacuum cleaner.”  “Now we know that white carpet is better than black if you have cats,” added Mr. Goldman, a 54-year-old business consultant who disliked all cats before he married Ms. Lehrer, and finds himself in the guest room when the two in his home are too active in the bed. “Marriage is a journey, and this is part of it.”  At least their cats are indoor animals. That means there is less risk of having mice and other critters deposited in the bed. Staying indoors, like most city cats do, also reduces the risk of fleas, ticks and other potential disease carriers.  Which brings us to dogs. Could all that slush they walk through and bring into bed at this time of year be a risk to health as well as to housekeeping?  “I’d say, just wipe them down and you’ll be fine,” said Lucy O’Byrne, a veterinarian at the West Village Veterinary Hospital in Manhattan. “As long as you have good flea and tick control, and keep your pet healthy the way most people do, you don’t have to worry.”  DR. CHOMEL, author of the C.D.C. study, doesn’t disagree. There is far more risk, he warned, with pet licks and kisses. If you have a wound or if your immune system is compromised, licking should be avoided. (Meaning, don’t let the dog lick you — the hazards involved in the other way around have not been researched.) It’s also not good for babies. And there have been cases of animals spreading resistant strains of staph infections and other diseases by licking cuts and wounds after surgery, so it’s not recommended that pets be allowed in bed then.  On the other hand, what would Patricia Garcia-Gomez have done without a dog in bed after major surgery? Six months after falling in love with her boyfriend, but not his territorial Rhodesian ridgeback, Sylvie (who made it clear that she didn’t like her turf being invaded by urinating in his apartment while staring into Ms. Garcia-Gomez’s eyes), she was recuperating when the Great Dane-size dog surprised her by joining her in bed. It was a great comfort.  “She’s been in bed with us since,” said Ms. Garcia-Gomez, who works in branding and lives in Manhattan (and is happy to provide Sylvie’s age, 8 ½, but not her own). “It can also be tricky, because when she stretches, she pushes us off. Humans only have two big legs, and she has four.”  Ms. Garcia-Gomez doesn’t worry about the dog’s giant licks, despite the fact that they present a real risk — just as the popular notion that dog saliva is cleaner than human saliva is a real myth.  “I’ll just continue to believe what I want to believe,” she said.  AND why not? Even if licking is risky, the risks might well be offset by the benefits, given the evidence suggesting that pets can increase longevity and boost the immune system.  “If the dog starts licking the baby too much, we discourage it,” said Alexandra Horowitz, author of the bestselling “Inside of a Dog,” and a psychology professor at Barnard, who sleeps with her toddler, husband and dog without worry. “But in general, if you’re a dog person, you live with dirt and other things that come in benign and less benign forms. I think the health risks are overstated. I say that if it’s mutually agreeable, just as it is between two people, then sharing a bed with a dog is fine.”  Even Cesar Millan, the hard-nosed dog trainer known for his TV series “The Dog Whisperer,” agrees, although he believes the dog should be invited up each night, just to show it who’s the real leader of the pack.  “Then choose the portion of the bed where the dog sleeps,” he writes in his book “Cesar’s Way.” “Sweet dreams.”  Sometimes, however, sweet dreams are not an option, as Tracy Rudd, an illustrator in Manhattan, has discovered. One man she dated years ago picked up her growling, nipping Chihuahua and tossed her out of the bedroom, later to find his clothes soaked in urine. When Ms. Rudd, 47, met her current husband, she said she knew he was the one because when he put his arm around her in bed during the night, causing her dog to growl and nip at him, he didn’t seem to mind.  “He just said he respected her for defending her space,” Ms. Rudd said.  As a result, the dog respected him and a lasting marriage was born.  Perhaps one day it will be the same for Ms. Ruttenberg with her upstate menagerie. “Although I’m starting to think it’s not likely,” she said.  Most gentlemen callers don’t even make it to the bedroom. One bolted when Ms. Ruttenberg, who has a total of 160 animals on her sprawling mountainside property, let a baby goat into the living room after Trixie, the pig, had already joined the visit.  “I thought he would find a little goat charming,” she said. “But after the pig, it was too much for him. Especially as the goat, Iris, was leaving droppings on the floor.”  Another date fled, after some wine and a soak in the hot tub under the stars, when Oola, one of the resident pigs (black, 150 pounds) charged and tried to bite him.  “And then, the last guy I had in the bed was freaked out by the rabbit,” Ms. Ruttenberg said. “He’s huge, and he got territorial seeing this guy in the room, so he started thumping and picking up his dish in his mouth and tossing it in our direction.”  “The truth is, with all my animals around me, I feel loved here, and I always have someone to come home to and someone who misses me when I’m away,” said Ms. Ruttenberg, who grew up on the Upper East Side and got her first pet, a dog, 20 years ago, after a terrible romantic breakup.  Ms. Ruttenberg’s mother frets that her daughter has put herself in the permanent zone of marriage ineligibility. But Ms. Ruttenberg is too busy making art, having fun and cooking for her animals (baked potatoes, squash, scrambled eggs with truffle oil for the pigs) to worry about it. As for the health risks of letting the animals sleep in her bed, she’s more concerned with making them sick than catching something from them.  “I had the flu and called the vet to make sure I couldn’t give it to Trixie,” she said.  The vet told her not to worry, she said.  If she called a dating coach, it might be another matter.  An article last Thursday about illnesses that can be contracted from sleeping with pets referred incorrectly to Chagas disease. It is spread by the insects known as kissing bugs or assassin bugs, not by fleas, and it can cause serious harm or even death, not just mild fever and fatigue.  A version of this article appears in print on February 17, 2011, on Page D1 of the New York edition with the headline: Warm Nights, Cold Noses. Order Reprints| Today's Paper|Subscribe
Sharing a mattress with pets has its risks: germs, crowding and rivalries. It also has its rewards: unconditional love.