The group of real estate agents finished the tour of a house that was about to come on the market and fled, holding their noses.

"It smelled like urine," sniffed one of the agents, who spoke anonymously because she wants to remain in the business. "I don't know what . . . they were doing in there. Some of these houses I don't think they ever opened a door or window. It's a big petri dish."

How is it, she wondered, that people can't smell their own homes?

Homes do reek, even the cleanest. Consider what happened when you came back from your last big vacation -- a couple of weeks in the jasmine-scented tropics, perhaps. You probably walked in the door, plopped the luggage in the foyer, and said something like, "Phew, it stinks in here!"

That smell? It's your very own house odor. It's a blend of your personal scent, your pets, the foods you prefer and the cleanliness (or lack thereof) of your possessions.

It's highly concentrated after the house has been closed up, said Charles Wysocki, a neuroscientist who investigates odor perceptions at the Monell Chemical Senses Center in Philadelphia and teaches at the University of Pennsylvania. "But even if you had someone air it out, you'd still notice an odor -- one you weren't aware of when you left."

Suddenly you're smelling your home as others do. You've "reset your olfactory system by being away," said Wysocki. "What they weren't appreciating before is that their own domiciles had odors that they weren't experiencing. They had this phenomenon of long-term adaptation."

He compares it to people who work in an odorous environment. "They become adapted to the point that they aren't even aware of it. If they work on Friday, go home for the weekend, and come in Monday; they still don't smell it."

Such ignorance can be bliss when you live in a stinky home, but not when you try to sell it. "Bad smells take $100,000 off your price," said our anonymous real estate agent.

She briskly ticked off a list of (especially) pet peeves: "Cat pee, dog smells, stale frat-boy sweats, jockstrap odor, cigarettes. Mildew? That's the worst one. I'd rather deal with cat pee. And it harms you physically. It really knocks you out. Potpourri? Can't do it. It's an olfactory attack. Scented candles, ugh."

In her own home she prefers the scent of fresh flowers. "Stargazer lilies, hyacinths and roses all have these wonderful smells," she said. "But some people do not like certain flowers. Paperwhites are one some people just hate."

Sometimes they don't like roses, either.

How you respond to various scents depends on how you were first exposed to them, Wysocki said. "If your first experience of smelling a rose as a very young child is walking through a garden hand in hand with your mother, it will be a memory much different from someone who experienced roses for the first time at the funeral of their mother. . . . It's very difficult to make predictions about what will be a pleasurable or acceptable smell to everyone out there."

Whether the odor is good or bad, women tend to smell it more intensely. "Women's perceptions of smell are generally better," Wysocki said. "Typically, women can detect odors at much lower levels."

Men and women also give off different smells. They have "a different body odor," the neuroscientist added. "It can be discriminated so that other people can tell them apart."

So perhaps a tiny spritz of male pheromone might attract women to a house?

"Not one I've heard before," he said with a laugh. "There is no 'sell your house faster' pheromone."

Even scents that you enjoy in one situation can be repellent in another. A perfume that delights at a party might be too personal in a home that you're considering buying.

Is there any generalization we can make about what makes a house smell good?

"Florals are generally well accepted," Wysocki mused. But for selling a home, "leather might be more appropriate."

Unless you have an aversion to horses.

"Well, there you go," he said. "Spearmint is very pleasant smelling and people chew spearmint-flavored gum. But spearmint is an unacceptable scent in England because it's used in horse liniment."

A highly unscientific, informal survey of a bunch of people who live mostly in the metropolitan area turned up a lengthy list of scent preferences, which on close examination broke down into two categories: food and nature.

It's not surprising that the aroma of cooking, and particularly baking, topped the list of scents that speak of home -- particularly bread, chocolate chip cookies, brownies and apple pie.

While it might dismay vegetarians, a roast in the oven was a turn-on for most. To stay on turf neutral enough for a vegan, you might try, as Cathy DeCenzo of Ashburn suggested, "onions, carrots and celery, the holy trinity saute."

Just forget fish. Fried, especially sauteed -- and definitely last night's -- is on the no list.

The smell of fresh flowers, pine, oranges, lemons, grass, cedar and laundry dried outside on the line were nearly as popular as food aromas. But with the exception of lemon furniture polish, which got nods, the scents have to be natural. The artificial reek of scented candles, room deodorizers and antiseptic "hospital-smelling" cleaners such as Pine-Sol and Lysol were turnoffs.

As for dislikes: Stale cigarette smoke topped the list along with pet odors, particularly cat urine and wet dogs. Dirty laundry, shoes, stale sweat and bathroom odors all were close seconds.

"Fresh and clean, clean and fresh. The vocabulary is very limited," said Carol Berning who researches scents for Procter & Gamble. Among her products is Febreze, a fabric deodorizer. "The thing that people really like is that it leaves the house smelling fresh, not stale. . . . Like a beautiful spring day when the windows are open; that's the kind of fresh people like."

To refine that elusive scent of fresh, the product was home-tested by "tens of thousands of people," said Berning.

P&G has also "done a fair amount of research among real estate agents," Berning said. They have said that "when people go looking at a house . . . they want to think of themselves living there. So what they don't want are odors that come from other people's families -- dogs, cats, babies . . . negatives. Like onions and sauerkraut. . . . We call it scent soup."

If you choose to add a stronger scent once the air is clean, that can be tricky, Berning said. "I probably wouldn't want to do something like flowers where some people like them and some don't. Most people like the smell of baking. . . . That is a very powerful homey smell."

"I'd love to see someone walk into a model home where a guy in a white hat was giving a cooking demonstration in the kitchen," said Craig Childress of Envirosell, a research company that studies "the behavior of people in retail environments . . . and model homes are part of retail."

Supermarkets are tapping into the lure of cooking aromas in a big way.

"It's not like the old days when you could smell the fish, the peanut grinder," Childress said. "They're pretty much wrapped up and sealed tightly. What's interesting to us is that cooking demonstrations are coming back in modern supermarkets. Management is not interested in selling the ingredients; what they are interested in is getting the olfactory sensation back."

He noted that many supermarkets are also adding another layer of temptation by revamping their circulation systems to vent bakery smells throughout the store. "The more involved you are with the five senses, the more you're going to want to purchase," he said.

Meanwhile, in model homes, people wander about "as they do in a museum, their hands behind their backs," he said. "It's usually pretty sterile. They'll have pictures of food and plastic models in the kitchens, but even in the show models there's never been an attempt to get cooking smells in the environment."

That's a big mistake, he maintains. "The kitchen is the most important part of the model home and people will come back to the kitchen and dining area and talk about the home as a whole."

And what of flowers and other home scents? "You have to be very careful with what you select. Anything applied unnaturally should be avoided," Childress said. There should be a connection between what you're smelling and reality. The smell of rain on a sunny day will certainly bother a person at some level.

"But there's some leeway. Fresh flowers in the dining room and the [artificial] smell of flowers in another room, there's a connection. Like the bakery smell on the other side of the store -- you're not thinking, 'Wow, they've got a sophisticated venting system.' "

Yet even the divine aroma of baking leaves the occasional home buyer holding his nose. "After looking at more than 70 houses last year, the smell of bread or cookies when I walked into a house was a red flag more than anything," Andy Schwarz said in an e-mail. "Call me jaded, but I know a Realtor . . . when I smell one. What were they staging . . . and what were they hiding?"

Only now, a year after he bought a place in Arlington, does he no longer feel manipulated by chocolate chip cookies.

On second thought, he realized scent did play a strong role in his purchasing decision. "Come to think of it, what did it for me was a good-smelling yard," he said in a follow-up message.

Just take a good whiff of the mulch before you buy it. Some of it . . . oh, my.