Preti is the accidental doctor, and he has more patients than he knows what to do with.
"He is unique," says Paul Fennessey, a pharmacology professor at the University of Colorado who tests urine samples from Preti's patients.
This isn't the kind of aroma that arises from not taking a shower. Those who visit Preti, at the Monell Chemical Senses Center, suffer from a rare metabolic disorder that can make them smell like decaying fish or garbage.
The disorder, called trimethylaminuria, has been found in fewer than 700 people worldwide. It can be so debilitating that some patients, shunned by society and undiagnosed by their regular doctors, become suicidal. Yet after some tests at Monell and a few changes in their diet, many eventually are able to control the symptoms and live a normal life.
The lab work and staff time cost at least $3,000, but Preti charges just $300. Monell, founded in 1968 near the University of Pennsylvania campus, is a research center and is not set up to deal with health insurance.
"If I billed like a lawyer, it would be substantial," Preti quips.
Preti, 62, feigns annoyance with the hundreds of calls that came in last year after he discussed the disease on network television. He claims that if he could get a medical doctor to take over his "practice," he gladly would.
But beneath a crusty Brooklyn-bred exterior, it is clear the scientist is devoted to his patients. When a Massachusetts woman came to see him last month, anxious that she was offending people with bad breath, he spoke to her with sensitivity.
Like some who find their way to the lab, she did not appear to have the metabolic disorder. Preti gives such patients what advice he can - recommending regular tongue-brushing or scraping, for example.
He ran some tests and took a few whiffs as the woman exhaled, then gently reassured her that the problem was minimal. After she left, he sniffed an absorbent pad that she had removed from her underarm. (It was normal.)
Says Preti's pal Fennessey: "This is really a labor of love."
When Mike was a baby, his mother would bathe him twice a day. Still, he smelled like fish.
"My grandmother would come over and say: 'You gotta wash this kid,' " he recalls.
As he grew older, the smell was a continuing source of anxiety. Schoolchildren and even strangers asked him why he smelled like dead fish. Teachers asked if he had neglected to take a shower.
He resorted to extreme measures: masking his odor with Bengay when playing sports, showering up to six times a day.
As an adult, he would sit at the end of a row at business conferences. A family doctor once took skin samples from his armpit, to no avail.
Then, on an airplane last summer, Mike read a magazine blurb about Preti, and it was a revelation.
"I wasn't crazy," says the 34-year-old, who lives in the Philadelphia suburbs and does not want to be identified for obvious reasons. "It was genetic, and I couldn't control it."
Actually, by avoiding certain foods, he can.
A nutrient called choline is especially prevalent in eggs, liver, certain seafoods and legumes such as soybeans. Bacteria break it down in the large intestine, producing a fishy-smelling chemical called trimethylamine.
In most people, the byproduct is oxidized by the liver and excreted as odorless waste. Those with trimethylaminuria, however, have a faulty version of a key liver enzyme. Though otherwise healthy, they are unable to oxidize the smelly trimethylamine, which is excreted in their urine, sweat, saliva and breath.
Some patients, including Mike, can keep their odor under control by avoiding foods high in choline. "I miss sushi in a big way," Mike says.
For others, Preti also recommends copper chlorophyllin complex, a supplement that appears to take up excess trimethylamine.
Antibiotics also can provide temporary respite. But Preti follows a specific treatment sequence and urges people not to try things on their own.
Even after all this, some patients still have a problem. Preti so far is at a loss for what to suggest, although he is looking for answers.
Preti showed an aptitude for science at his Brooklyn high school. His father, a Guatemalan immigrant of Italian descent, worked at a luncheonette and as a TV repairman to put him through college.
As a graduate student at the Massachusetts Institute of Technology, he analyzed dust samples from the Apollo 11 and 12 missions to the moon.
After landing a job at the Monell Center in 1971, his pursuit of chemistry took an earthier direction: bodily secretions. He won acclaim for studying pheromones and went on to discover the key chemical in human underarm odor.
In the late 1980s, a New York clinic referred a patient who complained of an occasional fishy taste in her mouth.
Preti recalled that Fennessey, whom he knew from grad school, had run across a similar case and had determined that his patient had trouble metabolizing trimethylamine. They spoke, and a collaboration was born.
The patients come to Philadelphia for three hours of consultation and tests. Their urine samples go to Colorado, where Fennessey's lab has developed a way to screen for the condition. Preti remains the only specialist in the United States who sees such patients, says Sandy Gordon, who saw Preti and later helped create the Trimethylaminuria Foundation.
Gordon, whose version of the disorder gives her a pungent smoky odor, almost moved out of her New York apartment in shame after fellow tenants incorrectly attributed her smell to marijuana smoke.
She went from specialist to specialist, and despaired after reading materials that suggested some patients imagine they have a disorder. Ten years ago, she heard of Preti.
"It was literally a turning point in my life," Gordon says.
More common than Gordon's smoky odor, but still rare, are the patients who smell like fish. Reports have appeared sporadically for centuries. In Shakespeare's The Tempest, Caliban is described as having "a very ancient and fish-like smell."
Yet only in the past few decades have scientists shed light on a cause. In 1972, researchers identified the lack of the correct liver enzyme as a culprit.
In 1997, British scientists found genetic mutations that lead to the disorder.
Others, including a Preti collaborator at Penn, have since found more. Steven Fakharzadeh, an assistant professor of dermatology at the medical school, screens blood samples from Monell patients. Preti's lab also is working on a way to test for the condition in saliva.
Some scientists have estimated the disorder to be as common as 1 in 10,000 people. Fakharzadeh says it is too soon to tell.
Meanwhile, Preti pursues the quest with a more personal piece of equipment: his nose. He has better-than-average olfactory powers (a Monell colleague tested him) but insists that bad smells bother him less than most.
That's good, because besides being a leading expert on human body odor, Preti also has studied the stink from large livestock farms.
Even better, he has a sense of humor. He recalls the time he spilled concentrated armpit extract on his shoes and socks. Not realizing the extent of the problem, he then inflicted the smell on fellow SEPTA commuters when riding home. His wife took a sniff, and the shoes got tossed, he says with a smile.
But when it comes to his accidental patients, the chemist is a serious listener.
"People are baring their souls," he says. Some have been coping well while others "curl up in the fetal position and want to die."
Either way, the man with a nose for a rare condition stands ready to help.
Contact staff writer Tom Avril at 215-854-2430 or firstname.lastname@example.org.