Smells like love: can your nose lead you to your Valentine?

Flowers, perfumes, and chocolates--people have long used these sweet-smelling objects to attract a mate each Valentine's Day. But could a dab of Hilary Duff perfume or Derek Jeter cologne really get your science lab partner to take notice of you, and not just your lab report?

Scientists have found that no two people smell things the same way. So what smells like roses to you may smell gross to others. Olfaction, or the sense of smell, does more than help you determine if a scent gets a thumbs-up or thumbs-down. It's an important sense that affects how you remember things or taste food. And yes, it does play a role in helping some animals zero in on love.

TAKE A WHIFF

From flowers to candies, almost everything on Earth emits an odor. Every object's odor is unique because each scent is made up of distinctly shaped odor molecules.

When you inhale near a bunch of Valentine's Day roses, the flowers' odor molecules enter your nose and travel to the olfactory epithelium (eh-puh-thee-lee-um), a membrane located at the roof of your nasal cavity (see Nuts & Bolts, below). Nerve cells in the membrane receive the odor molecules and translate them into electric signals. These signals then travel to the olfactory bulb in your brain, which transmits the information to the rest of your brain. Once your brain analyzes the signals, "it lets your body know what odor the molecules are linked to," says Craig Warren, a chemist at the University of California, San Diego. In this case, you recognize the odor as coming from roses and not someone's moldy gym socks.

There are more than 10 million nerve cells in your olfactory epithelium, and they can help you distinguish up to 10,000 different odors! While most humans are capable of sniffing out a large library of smells, not everyone agrees on what smells good.

SMELLS UNIQUE

Some people have a stronger sense of smell than others, says Christophe Laudamiel, a perfumer at The Sense of Smell Institute in New York. So their highly sensitive noses may be easily offended by strong odors.

Also, memories can cause you to love or hate a specific scent. For example, a whiff of a certain brand of cologne may remind you of a person in your life. The association of the scent with how you feel about the person may make you decide if the fragrance is a turn-on or a turn-off.

Furthermore, a bottle of perfume might smell great on one person but not as nice on another. "It's because of the person's background odor," says Laudamiel. Every person has a unique natural scent. Your mood, the foods you eat, and the medications you take, affect your body chemistry. In turn, they influence what you smell like. So how a perfume smells on you depends on how it blends with your body odor. In addition, your genes play a big role in how you carry a fragrance. These units of hereditary material determine traits such as hair color and complexion. Scientists have found that people with blond hair tend to have fair and dry skin. Dry skin does not hold on to perfume as well as oily skin, so the fragrance evaporates from the body more rapidly. A person with darker hair tends to have oilier skin. So a perfume usually smells stronger and lasts longer on a brunette than on a blond.

SMELLS ATTRACTIVE

It takes time to select a scent that you like and that also smells good on you. But what if you don't wear a fragrance--could you still get that cute boy or girl in science class to fall madly in love with you? After all, most animals never spritz on perfume, but they still manage to attract mates.

Studies show that many insects and rodents sniff out Mr. or Miss Right by detecting the pheromones (fe-row-mones) they emit. These are "chemical signals given off by one animal to be detected by another animal," says Charles J. Wysocki, a neuroscientist at the Monell Chemical Senses Center in Pennsylvania, who studies how the brain communicates with the body. Animals use the same cells that detect odor molecules to pick out some pheromones, even though these chemicals may not have any noticeable scent. Each individual's pheromones vary in chemical composition. Research shows pheromones have the power to cause one rat to become more drawn to another.

As for humans, pheromones are found in sweat. These chemicals can't induce love, but they can affect how people feel. In one study, Wysocki extracted underarm secretions from male volunteers. Then he had female volunteers sniff the sweaty secretions without telling them what they were. Test results showed that the pheromones caused the women to feel less stressed. Wysocki and other scientists are not sure why this was, but it does suggest that pheromones can influence people's moods and behaviors.

No one has invented a magic love potion yet. But it's a good bet that you'll appear more attractive if you smell like flowers or spring breeze, and not two-week old laundry.

nuts & bolts

Follow the steps below to learn how your sense of smell works.

(1) A rose emits odor molecules

(2) As you inhale, the molecules enter your nostrils.

(3) The odor molecules travel to a membrane called the olfactory epithelium. There, odor receptors, or nerve cells, translate the molecules into nerve impulses (electric signals).

(4) The olfactory bulb, which is a part of the brain, receives the impulses. It transmits the signals to the rest of your brain, which analyzes what odor the molecules are linked to.

[ILLUSTRATION OMITTED]

SMELL WHAT YOU EAT

A box of heart-shaped chocolates, yum! Guess what? You'd taste almost nothing without your nose. That's because the sense of taste is tightly tied to olfaction.

The taste receptors on your tongue can only detect sweet, salty, sour, bitter, and "umami"--or savory--sensations. A large percentage of the "taste" of complex foods or drinks comes from the odor molecules that give them their scent. These molecules float up the back of your throat to your nasal cavity. There, your odor receptors go to work to help you detect and enjoy the rich aroma of chocolate.

Ever notice when you have a cold, everything tastes bland? That's because the mucus in your nose blocks the odor chemicals from reaching your smell receptors. Too bad you can't stuff up your nose to avoid tasting the cafeteria's mystery meatloaf.

web extra

Sniff out more olfactory science at: www.senseofsmell.org

Smells Like Love

PRE-READING PROMPTS

Jump-start your lesson with these pre-reading questions:

* Research shows that the human nose can detect more than just smells. It can tell which direction an odor comes from What other sensations can the sense of smell help detect?

* According to the Fragrance Foundation, to make a scent last, it should be applied directly onto the skin--from the feet to the shoulders. That's because fragrance rises. If you only dab fragrance behind the ears, the scent will rise and disappear faster than if you apply it to the lower points of your body. What other factors may affect how long a scent lasts on a body?

CRITICAL THINKING:

* Olfaction is strongly tied to memories and emotions. According to scientist at the Sense of Smell Institute, "people recall smells with a 65 percent accuracy after a year, while the visual recall of photos sinks to astral 50 percent after only three months." Can you think of some examples that support this statement?

CROSS-CURRICULAR CONNECTIONS:

HISTORY: Have students do research and report on the history of Valentine's Day, and how its customs have changed over time.

RESOURCES

* This Web site contains both teachers' and students' guides to the science of olfaction: http://faculty.washington.edu/chudler/chems.html

* To learn more about Charles J. Wysocki's research on pheromones, visit: www.upenn.edu/pennnews/article.php?id=47

Name:

DIRECTIONS: Fill in the blanks to complete the following sentences.

1. -- is the term meaning sense of smell.

2. Every object's odor is unique because each scent is made up of distinctly shaped --.

3. The olfactory epithelium is a -- located at the roof of your nasal cavity. It contains more than 10 million odor receptors, or --.

4. Animals such as rodents emit --, or chemical signals given off by one animal to be detected by another animal. This chemical can be found in human --.

5. The taste receptors on your tongue detect these five sensations: --, --, --, --, and --.

ANSWER

1. olfaction 2. odor molecules 3. membrane; nerve cells 4. pheromones; sweat 5. sweet, salty sour, bitter, umami

HANDS-ON SCIENCE

(No Lab Required)

After reading "Smells Like Love" (p. 8), try this activity to test your sense of smell.

PREDICT

Many animals--for example, honeybees and dogs--have a keen sense of smell. Can you use your sense of smell to distinguish between different scents, and to detect similar ones?

MATERIALS

Mystery-scented film canisters* *Teachers: See this issue's Teacher's Edition for details.

PROCEDURE

1 Your teacher will place one open film canister in each corner of the room. These film canisters each contain one of four different mystery scents.

2 Next, your teacher will give each student a film canister that contains a scent.

3 Wave your hand back and forth over your canister to waft the scent toward your nose. Note: You are not allowed to talk during this experiment or tell anyone what odors you smell.

4 Other students in the room have a canister containing a scent similar to yours. Your job as a "honeybee" is to walk around the room to locate these students. Do this by wafting the scents in other people's canisters toward your nose.

5 As you find people with matching scents, begin to form a group.

6 Once you are confident that you have found all of the group's members, your group needs to find the corner of the room that contains your honybee colony's "hive."

7 As a group, stop by each of the four corners and waft the smell of the corner's canister toward your nose. If its odor matches that of your canister, you have found your colony's hive. If not, continue to each hive until your group locates its hive.

CONCLUSIONS

1. As a class, discuss if some smells were easier to find matches for than others. If so, which ones?

2. Would this experiment be more or less difficult if you were to perform it outside on a windy day? Explain your answer.

Teacher's Notes for Hands-On Activity

To make the mystery-scented film canisters, you'll need: cotton balls (one for each student, plus four additional ones) * vanilla extract * vinegar * almond extract * lime juice * film canisters (one for each student, plus four additional ones) * red permanent marker * black permanent marker * masking tape

To do on the night before the activity:

1. Divide your cotton balls into four groups.

2. Soak one group of cotton balls in vanilla extract, a second group in vinegar, a third in almond extract, and a fourth in lime juice.

3. Place one cotton ball into each film canister, Then place a lid on each canister.

4. Code the canisters so that you--and only you--know which scent each of the canisters contains. For example: Put a small red dot on the bottom of the vanilla-scented canisters: a tiny piece of tape on the bottom of the vinegar-scented canisters; a piece of tape with a tiny black dot on the base of almond-scented canisters: and do nothing to those canisters that smell of lime.

To do on the day of the activity:

1. To begin the activity, remove the lids from the canisters.

2. Place one vanilla-scented canister in one corner of the room, a vinegar-scented canister in a second corner, an almond-scented canister in a third corner, and a lime-scented canister in the remaining corner.

Conclusions:

1. Answers will vary.

2. It would be more difficult to do this experiment outdoors and on a windy day. As you waft your hand over the canister, the wind might carry the scent away from your nose. The wind could also carry outdoor scents, such as grass or flowers, to your nose. This makes it more challenging to pinpoint the scent in each canister.