THE NOSE KNOWS

THE NOSE KNOWS

The stinking fuss about stench in two city barangays (formerly barrio, in Spanish) reminds me of an anecdotal court case whose outcome swung on the testimony of an expert witness. The prosecution witness had a reputed ability to distinguish odors of a wide range of chemicals and substances. He was to identify and pinpoint the source of the foul and obnoxious odors permeating a certain locality.

The wily defense team neutralized the expert’s testimony with simple cunning. Asked to identify two common liquids contained in separate receptacles, the expert sniffed the first substance proffered and promptly identified it as gasoline, but thereafter failed to identify the second. The defense had deadened his sense of smell with the first whiff. Chicanery may win court cases, but firms polluting the air with repulsive vapors emanating from putrid wastes and effluents to save costs cannot mask or neutralize the wafting stink.

Household deodorants being marketed do not really remove odors as ads imply, but merely mask the unwanted odor with a stronger aroma. There are three basic ways to get rid of undesirable odors: masking them with stronger scents, such as the ubiquitous lemon and pine fragrances; chemically dissolving or absorbing them with activated charcoal, baking soda or silica gel; and numbing out the nose. In the past, air-freshener products in the last category used formaldehyde or its solid version, paraformaldehyde, which is known as both poisonous and carcinogenic. The Monsanto company later developed a somewhat less lethal nasal anesthetic (the precise formulation is secret), which has since been incorporated into some air-fresheners along with the usual masking fragrances.

Some firms deny making use of a nasal anesthetic, saying that their products employ a combination of masking fragrances and odor counteractants which is curiously, the similar-sounding term malodor counteractant used in scientific journals, a code word for nasal anesthetic.

SENSE OF SMELL

The sense of smell is a potent means of animal communication. Many animal species emit smell signals called pheromones for luring mates, marking territory, deceiving enemies, or detecting prey and predators.

Compared to animals, humans are poor sniffers. The rabbit has 100 million cells in its nose used for smelling, and German shepherd dogs have 200 million, 44 times the number that humans possess. The intense sniffing ability of dogs (canines or its militarized homophone K-9) is employed by police to sniff and detect contraband drugs and explosives or track fugitives or lost children. A late news item carried the story of Scooby, an ace sniffer dog about to retire. The 7-year-old Labrador was so successful that drug dealers took out a contract on his life and that of his owner.

Late news (March 2008): Wine Taster's Nose Insured for Millions. His schnoz is not to be sniffed at. The nose of leading European winemaker and taster Ilja Gort has been insured for euro5 million ($8 million), Lloyd's of London said. Gort, 47, said his nose is essential for him to produce top quality wines at his Chateau de la Garde vineyard in the famous Bordeaux region of France, so he got it insured. The custom-made policy covers Gort for the loss of either his nose or his sense of smell and has some unusual conditions.

The insurance contract includes a list of what Gort considers "old-fashioned rules" to protect his nose. The Dutchman is not allowed to ride a motorcycle or be a boxer, knife thrower's assistant or a fire-breather. "I may not fight against Mike Tyson," Gort said.

To humans, a chemical compound to possess an odor must pass into the nasal cavity, directly above which are olfactory bulbs with projecting hair (tiny nerve fibers) that receive smell impulses and relay them to the brain. The exact mechanism is not known. One theory is that the aromatic molecules dissolve in the fluid of the cavity lining and bathe the sensory cells. Another is that gas comes into direct contact with the sub-microscopic cell hairs that penetrate the mucous layer.

The ability to smell a particular substance depends on the concentration of its presence in the air. Higher temperatures and moisture intensifies the smell. Thresholds of detection for different substances vary. For example, expressed in milligrams per thousand cubic meters, for a large room of 35,000 cubic feet in volume are:

feces (skatole) is 0.0004,

rotten cabbage (mercaptan) is 0.04,

rancid butter (butyric acid) is 1.0.

Malodorous mercaptan, considered the worst odor ever compounded, was at one time added to cooking gas to give warning of dangerous leaks. This practice was discontinued when odorous liquid petroleum gas (LPG) in cylinders was marketed.

The paucity of odor words in the vocabulary of most languages is obvious when attempting to describe a scent. A redolent thing assumes the bouquet of a flower or fruit, such as jasmine, rose, orange, lemon, apple, vanilla, and vulgar terms for substances reeking obnoxious odors: rotten egg, fishy, flatus.

Though many aromas are described in terms of fruit scent, there is one fruit that defies description with widely divergent and passionate views expressed, ranging from highly appreciative to deep disgust. The durian fruit that grows in Southeast Asia’s equatorial belt, (the Sulu archipelago in the Philippines) has a flavor and aroma that elicits the full spectrum of odor: cream-cheese, onion-sauce, sherry-wine, pig-shit, turpentine and onions garnished with a gym sock, French custard passed through a sewer. These are the kind words. The aroma of the fruit is so powerful it is forbidden in tourist areas and in public transport of many countries.

Odors often attain meanings that noses cannot sense. Fishy means an article or action that is questionable or suspicious. Stink is a public outcry over something offensive. And if something “stinks to high heavens”, the scope of suspicion becomes enormous, blatant, and flagrant.

CHEMISTRY MAGIC

Modern chemistry has made great strides in two fields affecting human lives: in food flavors and in perfumes and aromatics. Analysis of chemical components of the aromatics in foods and botanical fragrances enabled chemists to synthesize chemicals mimicking the scent of practically all flavors and fragrances.

In food labs, essential oils of various foods can be duplicated – alcohols (menthol), aldehydes (cinnamon), esters (lavender), ethers (aniseed), ketones (dill), phenols (cloves). These synthetics are now routinely added to natural products as blend or augmentation, and even to replace entirely as imitation.

The other field of fragrance magic is in perfumes, a word derived from Latin per fumus (through smoke). If wild animals have their pheromones, sophisticated man, or more aptly, alluring woman, has perfume as lure.

The art of perfumery is traced as far back as the pharaohs of ancient Egypt. Its history mentions the scents of Cleopatra, the frankincense and myrrh of the three Magi bringing gifts to the babe in Bethlehem, and both Napoleon and Josephine are known fanciers.

The perfume business has spread to practically all countries as ingredient suppliers or as users of colognes and eau de toilette. A good perfume is said to have 10 to 50 ingredients blended from natural oils, synthetics (aromatic chemicals), and fixatives to bind the mixture. Animal fixatives, whose purpose is to slow down the evaporation of the more volatile oils, includes ambergris from whales, musk from musk deer and civet from wildcats. The fragrance of ylang-ylang is the Philippine contribution, said to be an ingredient of renowned perfumes made by Yves St. Laurent.

There are five standard methods of capturing essences from nature: distillation, expression, maceration, enfleurage, and volatile solvents process. But there are fragrances such as the lily and lilac that cannot successfully be made to yield their natural oils. Modern chemistry intervened, first probing the composition of natural fragrances and eventually compounding substances resembling those of nature. One such chemical was used in a popular brand: Chanel no. 5.

The creation of a good perfume is finally the result of the artistry of a master perfumer blending by trial and error for as long as a year, and adding such ethereal qualities as appeal, taste, originality, and theme.

An amusing story was in the news recently. A cheap imitation fragrance named Viagra, a concoction of ingredients that even its owner does not know, has been sued by the makers of the popular drug with that patented name. Some people just do not accept the saying that imitation is the sincerest form of flattery.

Despite the huge market of fragrances in the food and perfume fields, they share a miniscule one-fifth of total manufacture. Most are used to scent consumer goods such as medicinal ointments and unguents, detergents, and even cars to provide the illusion of freshness.

AROMATHERAPY

Aromatherapy is the practice of using volatile plant oils, including essential oils, for psychological and physical well-being. Perfume oils are not the same as essential oils. Perfume oils and fragrances contain chemicals that do not provide the claimed therapeutic benefits of essential oils.

The modes of application of aromatherapy, predominantly topical applications for general massage, baths, compresses, therapeutic skin care, but also include aerial diffusion for environmental or aerial disinfection, direct inhalation for respiratory disinfection, decongestion, expectoration as well as psychological effects, and

oral, rectal, vaginal interfaces for infection, congestion, parasites, perfumery for body fragrancing, anointments

In the English-speaking world, practitioners tend to emphasize the use of oils in massage, and aromatherapy tends to be regarded as a complementary modality at best and a pseudoscientific fraud at worst.

One of the most comprehensive investigations done to date on aromatherapy failed to show any improvement in either immune status, wound healing or pain control among people exposed to two often-touted scents. While one of two popular aromas touted by alternative medicine practitioners – lemon – (also the favored scent for dishwashing liquid soap and deodorants) did appear to enhance moods positively among study subjects, the other – lavender – had no effect on reported mood, based on three psychological tests.

Neither lemon nor lavender showed any enhancement of the subjects’ immune status, nor did the compounds mitigate either pain or stress, based on a host of biochemical markers.

DOWNWIND OF SKATOLE

A favorite expletive of General “Bull” Schwarkoff (B.S.) of desert Storm fame was “bovine scatology”, abbreviated B.S. (commonly known as bullshit). His use of the term was military parlance, not in reference to odors. But whosoever gets downwind of skatole will surely get the urge to use an equally expressive civilian expression.

I once had a lively discussion with an agent of a food company who was trying to persuade our neighborhood to allow his company to set up shop nearby, on a lot that encroached into an area declared as a residential zone. His plea was based on the non-pollutive quality of the product (a food item) and the unobtrusive nature of the processing (repackaging).

The attempt to dialog was in itself extraordinary, in contrast to the habitual arrogance of firms contemptuous of community sensitivities. After his spiel, I asked a pointed question: if the product is organic and will therefore spoil, and spillage is unavoidable, what assurance can the company give that the sanitation and cleanup procedures will prevent putrification, considering the lack of a nearby public sewer for dumping their waste water? He has not returned with an answer.

The dialog may have averted a potential incompatibility conflict and discord similar to the furor caused in Barangays Gusa and Tablon. It was also a sign that public displeasure over effluvia has made business firms aware that they can no longer thumb their noses at public feelings. For whenever there is aroma waft in the air, be it from dung or lady fair, the nose knows.

WATER, fluid more precious than oil

WATER, fluid more precious than oil

Chemically, water is a nearly universal solvent. Biologically, it is the dominant constituent of living matter. Physically, it is virtually the only common substance that occurs on our planet as gas, liquid and solid and so defines many of the characteristics of our world. A view of Earth’s surface from outer space is not earthen at all but watery.

Yet finding enough water is a difficult and divisive problem for our society. Most of us take water for granted until nature reminds us otherwise. The latest reminder was the delayed onset of the rains in mid-2007 in the northern Philippines that created such anxiety and panic that officials scrambled some planes skyward to cloud-seed salt. It abated the fears but produced little moisture. Nature, in this instance in the form of the seasonal Southwest Monsoon withheld the rain bearing clouds.

A water shortage is a frustrating problem. Decades of cloud-seeding studies in dry locations around the globe have only confirmed that there is very little meteorologists can do when nature stubbornly withholds rain. Those Air Force planes scattering dry ice or silver iodide calms public anxiety but little moisture to wet the earth. Engineers build dams to collect water or levees to contain overflowing river banks but can’t make one drop of water grow into two.

Water sustains life, not only to the human species but also other organisms that cause illness to humans. Water borne diseases, most commonly diarrhea and typhoid, are caused by water contaminated accidentally or by carelessness. Circulating in nature’s hydrologic cycle (cloud-rain-surface or ground water) the fluid is abiotic but is compromised by man-made devices or pollution.

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Clean water plays another role in human health: hygiene.

Q & A:Men are supposed to wash their hands after urination?

A Harvard man and a Yale man are at the urinal. They finish, zip up, then the Harvard man proceeds to the sink to wash his hands, while the Yale man immediately makes for the exit. The Harvard man says, "At Hah-vahd they teach us to wash our hands after we urinate."

The Yale man replies, "At Yale they teach us not to piss on our hands."

Question: why is it customary for males to wash their hands after urination? I bathe daily and wear fresh underpants, so how does my penis get dirty? It's not like I dig a ditch with it. However, my hands might get dirty from daily activities. Is it not more sensible then to wash my hands before touching my clean penis? Is post urination hand washing a throwback to the bad old days, when sex was "dirty" and so, by extension, were sex organs?

Answer: Good joke; common (but stupid) attitude; rank (but important) topic. Some facts:

The purpose of washing is not to get pee off your hands.

No amount of washing will make you clean.

Your boxer-shorts region--from belly button to mid-thigh--is crawling with germs known as coliform bacteria. These bacteria originated in your intestine, and some of them are deadly. Recall the punji stakes, sharpened sticks that the Vietcong concealed point up along trails and daubed with excrement. Stepping on one, you had a good chance of contracting a fatal infection. Similarly, an otherwise not-so-serious gunshot or knife injury could kill you if it perforated the intestine and allowed coliform bacteria to spread around your abdomen.

What you may not know is that washing will not make the coliform bacteria go away. They're holed up in the pores of your skin and nothing short of sandblasting--certainly not your morning shower--is going to get them out. Showering merely gets rid of the ones that have strayed onto the surface. The bacteria won't do much harm if they stay put, but when you urinate your fingers come in contact with Mister P. long enough for the coliform bacteria in your pores to hop aboard. Your fingers subsequently touch lots of other infectible items. If you don't wash your hands with soap and water (soap gets rid of the skin oil that the bacteria stick to). . .

It now dawns on you: jeez, if merely touching my privates is enough to transmit bacteria, it doesn't matter if I pee or not! Urine is actually fairly sterile. There are reports of it being used during wartime in poor countries as a sort of battlefield disinfectant. The lesson to draw from this, however, is not that you can go forth dripping, but rather that just because you didn't pee on your fingers doesn't mean you can skip washing up.

Washing Hands Best

The largest, most comprehensive study ever done comparing the effectiveness of hand hygiene products shows that nothing works better in getting rid of disease-causing viruses than simply washing one’s hands with good old-fashioned soap and water.

Among the viruses soapy hand washing flushes down the drain is the one that causes the common cold. Other removable viruses cause hepatitis A, acute gastroenteritis and a host of other illnesses. A separate key finding was that waterless handwipes only removed roughly 50 percent of bacteria from volunteer subjects’ hands.

"We studied the efficacy of 14 different hand hygiene agents in reducing bacteria and viruses from the hands. No other studies have measured the effectiveness in removing both bacteria and viruses at the same time." said a public health epidemiologist with the University of North Carolina Health Care System and the UNC School of Public Health.

For the first time, too, the UNC researchers tested what happened when people cleaned their hands for only 10 seconds. That represented the average length of time researchers observed busy health-care personnel washing or otherwise disinfecting their hands at work. Previous studies have had people clean their hands for 30 seconds or so, but that’s not what health-care workers usually do in practice, and the study wanted to test the products under realistic conditions.

Anti-microbial agents were best at reducing bacteria on hands, but waterless, alcohol-based agents had variable and sometimes poor effects, becoming less effective after multiple washes. For removing viruses from the hands, physical removal with soap and water was most effective since some viruses are hardy and relatively resistant to disinfection.

A report on the findings appears in the March issue of the American Journal of Infection Control. Authors are professors of medicine and epidemiology at the UNC schools of medicine and public health; a professor of environmental sciences and engineering in public health; and medical technologist. A Duke University biostatistician, helped analyze the data.

"These findings are important because health-care associated infections rank in the top five causes of death, with an estimated 90,000 deaths each year in the United States," the author said. "Hand hygiene agents have been shown to reduce the incidence of health-care associated infections, and a variety of hand hygiene agents are now available with different active ingredients and application methods.

"Our study showed that the anti-microbial hand washing agents were significantly more effective in reducing bacteria than the alcohol-based handrubs and waterless handwipes," he said. "Our study also showed that, at a short exposure time of 10 seconds, all agents with the exception of handwipes demonstrated a 90 percent reduction of bacteria on the hands."

Alcohol-based handrubs were generally ineffective in demonstrating a significant reduction of a relatively resistant virus. While the use of alcohol-based handrubs will continue to be an important infection control measure, it is important to recommend or require traditional hand washing with soap and water throughout each day.

Researchers first had volunteers clean their hands and then contaminated their hands with Serratia marcescens, a harmless bacterium, and MS2 bacteriophage, a virus comparable to, and substituted for, disease-causing organisms. After that, scientists had the subjects clean their hands with various agents and measured how much of the bacteria and virus remained afterwards.

Adapted from materials from University Of North Carolina School Of Medicine.

Related Stories

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Hand Sanitizers No Substitute For Soap And Water (Feb. 21, 2000) — Instant hand sanitizers may not be everything consumers expect, according to a Purdue university professor who teaches sanitation practices for food service ... > read more

Simple Measures Can Reduce Spread Of Respiratory Viruses (Oct. 18, 2007) — Blocking transmission of respiratory viruses is an important part of halting spread of disease if an epidemic breaks out. Good hand-washing with normal soap and water are effective ways of containing ... > read more

When It Comes Fighting To C. Difficile, Try Soap And Warm Water (Sep. 25, 2007) — Hospitals world-wide battle infections on a daily basis. One of the most difficult bacteria to combat is Clostridium difficile. Researchers check out many control methods and gave the highest honors ... > read more

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If You Don't Want To Fall Ill This Christmas, Then Share A Festive Kiss But Don't Shake Hands (Dec. 19, 2007) — We've all heard people say 'I won't kiss you, I've got a cold'. But a new report warns that we may be far more at risk of passing on an infection by shaking someone's hand than in sharing a ... > read more

At Home

Most studies on hand washing focus on medical and food service workers. But the American Journal of Infection Control focuses on washing hands at home as a way to stop infections from spreading. Several studies show hands are the single most important transmission route for all types of infections.

Even though most people know to wash their hands after using the toilet or handling a diaper, studies suggest many people are still ending up with germs, particularly those spread by feces, on their hands after leaving the bathroom or caring for a baby.

One study looked in homes of infants recently vaccinated against polio. After vaccination, the virus is known to shed in the baby’s feces. Researchers found the virus on 13 percent of bathroom, living room and kitchen surfaces. While the virus from the vaccine didn’t pose a health risk, the study shows how feces-borne viruses can travel through the home.

Another study found that in homes where salmonella cases had been diagnosed, the bacteria were still lurking in toilet bowls three weeks after the outbreak. Water splashing on the toilet seat was a source of contamination.

Doorknobs, bathroom faucets and toilet flush handles are key sources of germ transmission in the home. That’s why people should focus on cleaning such surfaces regularly and always wash hands after touching them. In one study, a volunteer touched a door handle that had been contaminated with a virus. He then shook hands with other volunteers, and further tests showed he had spread the virus to six people.

The study authors note that the timing of hand washing is key. It’s obvious to wash hands after using the toilet, after sneezing or before eating or handling food. Other crucial times for hand washing are after changing a diaper or cleaning up after a pet, or after touching garbage cans, cleaning cloths, cutting boards, dish rags and utensils that may have come into contact with raw food.

While it may be hard to believe that something as simple as regular hand washing can make a difference in your family’s health, consider what happened in Hong Kong during a 2003 outbreak of SARS, a severe and potentially deadly form of viral pneumonia. The outbreak triggered extensive public and community health measures promoting basic hygiene, including regular hand washing. Not only was the SARS outbreak contained, but other cases of respiratory illnesses, including the flu, dropped sharply.

Comments

Sound advice. I would add that we should avoid touching our mouth, nose, and eyes with unwashed hands. If you can’t wash your hands, use a tissue, and make sure the part that touched your hands does not touch your face. — Posted by Jack F. Bukowski, MD, PhD

I would like an answer to the paper towels vs. electric hand dryer controversy. Restrooms with hand dryers all have signs proclaiming that they are the best hygienic choice. However, restrooms with paper towels often have signs explaining how one should first turn off the sink faucets with the towels and then dry the hands. Actually, this makes more sense to me, especially if one also exits the room using the paper towel to open the door. — Posted by Michael Hendler

It is important to emphasize the obvious. Washing hands, beware of toilet handles, door knobs, etc. all apply to every situation outside the home as well. Public restrooms of all sorts, and most particularly in airplanes, the most dangerous place to be in terms of danger of infection (after hospitals , of course). — Posted by Richard Gustafson

I used to work in an office with about twenty other people. One of my co-workers commented on my use of a paper towel to open the bathroom door, teasing me about ‘not trusting’ my co-workers to wash their hands. I just smiled and said, “It’s habit, especially during flu season.” Yes, flu germs are often airborne, but people don’t wash their hands after they blow their noses, cough, or sneeze, and they leave those germs on everything they touch. — Posted by Rowan

… people who sneeze into their hands. I’ve seen many many people who would otherwise consider themselves to be extreme hygienic do this in public - and then proceed to touch everything around them as if nothing has happened. If you don’t have a tissue, spare the rest of us and sneeze into your shirt or jacket sleeve, not your hands! — Posted by Dan Schenck

How to wash one’s hands properly is also very important. In the public washrooms we’re having increasing installation of automatic water taps, soap dispensers using sensors. This is good. However, the provision of air blowers for hands drying means paper towels no longer provided. Users have to find way to pull open the exit door. Perhaps consideration should be given to provision of automatic exit door or simply taking it down if circumstances allow.— Posted by Kevin Shum

Does anyone know the difference in effectiveness in reducing transmission with antibacterial soaps vs. regular soaps? Like my hesitation to use antibiotics quickly, I’ve assumed antibacterial soaps will encourage the presence of more resistant bacterial and thus have avoided using them — but I’d love to know more from any experts on the subject.



From TPP — I’ve written about this topic. there is no difference in effectiveness between handwashing with regular soap or antibacterial soap, although there is a theoretical risk of contributing to bacteria resistance when you use an antibacterial soap product. (The article is reproduced below.)

Germ Fighters May Lead to Hardier Germs

By TARA PARKER-POPE Published: October 30, 2007

Reports of schoolchildren dying from infections with drug-resistant bacteria are enough to send parents on an antimicrobial cleaning frenzy.

But before you start waging your own personal war on single-celled organisms, be warned. Many household and personal cleaners contain ingredients that could make the resistance problem worse.

Today, hundreds of soaps, hand lotions, kitchen cleansers and even toothpastes and mouthwashes include antibacterial agents. One of the most popular is triclosan, which has been used not only in cleaners but also to coat toys, cutting boards, mouse pads, wallpaper and even dog bowls.

The temptation to blanket our families with antibacterial protection has been fueled by scary news reports about a deadly bacteria called CA-MRSA, which stands for community-acquired methicillin-resistant Staphylococcus aureus. Two otherwise healthy children — a seventh grader in Brooklyn and a high school football player in Virginia — died in recent weeks from MRSA infections.

The general advice for avoiding infection is basic hygiene — washing hands or using alcohol-based sanitizers, keeping scrapes covered until healed and refraining from sharing personal items like towels and cosmetics.

But some recent laboratory studies suggest that antibacterial products containing triclosan may not be the best way to stay clean. Instead of wiping out bacteria randomly, the way regular soap or alcohol-based products do, triclosan may inhibit the growth of bacteria in a way that leaves a larger proportion of resistant bacteria behind, according to lab studies at Tufts and Colorado State Universities, among others.

In fairness, none of the research has shown this effect in the real world. In fact, two randomized studies comparing people who used triclosan hand soaps with people who used plain soaps found no evidence that triclosan contributed to bacteria resistance. The soap industry says these results are far more compelling than the controlled lab studies.

But Allison E. Aiello, an assistant professor of epidemiology at the University of Michigan School of Public Health, says the laboratory evidence against triclosan is compelling enough to raise questions about the products. More meaningful, she says, is that several studies show that antibacterial soaps sold to consumers are no better than plain soaps in terms of reducing illness or the count of bacteria left on hands.

“Given that there doesn’t seem to be a benefit, I think it warrants further evaluation,” said Dr. Aiello, whose review article on antibacterial soaps was published last month in the medical journal Clinical Infectious Diseases. “We should be questioning use of these products.”

Soap companies say the worry about triclosan takes the focus away from the real culprit: the abuse of antibiotics and the need for better hygiene in general. “The last thing we want to see is people discouraged from using beneficial hygiene products,” said Brian Sansoni, a spokesman for the Soap and Detergent Association.

In any given colony of bacteria, some portion will often have a natural resistance to antibiotics. The resistant germs might contain genetic variants that give them stronger cell walls, or pumps that allow them to spit the antibiotic back out. They survive the antibiotic onslaught, and with the susceptible bacteria out of the way, naturally resistant strains can thrive. Not only do they multiply, but some can also share their resistance with other bacteria and collect new resistance traits over time.

Natural resistance happens on such a small scale that it is generally not a health worry. But when antibiotics are overused — either by individuals or when farmers add them to animal feed — the effect is amplified. “You’re going to have this exaggerated, snowballing effect of resistant bacteria multiplying all around you,” said Marlene Zuk, a biology professor at the University of California, Riverside, whose book “Riddled With Life” discusses the proliferation of antibacterial cleaners and personal products.

The question about cleaners containing triclosan is whether the agent kills germs randomly or whether it promotes the same selection pressures that can lead to antibiotic resistance. The worry is not that bacteria might become resistant to triclosan. The fear is that the same bacteria that resist triclosan can also resist certain antibiotics. And a handful of lab studies have suggested that triclosan may select for resistant bacteria.

“Here you have a substance that has been widely used in hospital settings and household settings,” said Herbert P. Schweizer, associate director for research at the department of microbiology, immunology and pathology at Colorado State University, who conducted some of the lab studies showing triclosan resistance. “The exposure to this widely used antimicrobial caused emergence of multidrug resistance in laboratory strains.”

That studies of triclosan use haven’t shown a resistance problem in the community doesn’t mean it won’t happen, said Dr. Stuart B. Levy, a microbiology professor at Tufts who is president of the Alliance for Prudent Use of Antibiotics.

“I’m the first to say we haven’t seen a difference yet in the home,” Dr. Levy said. “We know from antibiotic data that if it happens in a lab it will eventually happen outside the lab.”