Chemicals that make babies smell sweet and teens smell 'goat-like' revealed

For science, volunteers sniffed out odorous chemicals in the armpit sweat of babies and teenagers. Perhaps unsurprisingly, they found that young children smelled like flowers and teens smelled like goats — but now, we know which chemicals are responsible for each of these odors.

Many of us are familiar with babies' sweet scent, but we may wince while catching a whiff of a teen who's skipped out on that day's deodorant. Previous studies have also found that parents prefer the odors of babies to those of teenagers, which may somewhat influence their affection toward their children. Intrigued by the role scent plays in relationships, lead study author Helene Loos, an aroma researcher at Friedrich Alexander University in Germany, aimed to explore how BO changes throughout life.

In the research, published March 21 in the journal Communications Chemistry, Loos and her colleagues provided 18 young children, ages 0 to 3, and 18 teenagers, ages 14 to 18, with T-shirts with cotton pads sewn into the armpits. After the participants wore the tees for one night's sleep, the researchers sampled smelly substances that had soaked into the pads.

Using gas chromatography, a technique that splits up chemicals with different properties, the researchers separated and detected the individual odorants in each BO sample. Then, they asked volunteers to smell and describe each chemical's scent.

Related: Super sensitive to BO? Maybe blame your genes

Forty-two odorants were detected, with both age groups producing most of them, Loos told Live Science. Note that a single odorant can set off many smell sensors in the nose, and combinations of odorants can trigger unique and complex patterns of activity that differ from what one odorant does alone. Nonetheless, the component scents in a given bouquet influence whether it smells bad or good to the sniffer.

"We were not surprised by the overall findings, but it was very interesting to see the rich variety of compounds," Loos said of the odorants detected. Among these, a group of chemicals called aldehydes was the most diverse, giving off "cardboard-like," "deep-fried" and "nutty" aromas, for example.

BO from both age groups also contained carboxylic acids, a class of organic compounds. Some were pleasant, giving off "fruity" or "dried plum-like" notes. Others were less so, smelling "cheesy," "musty" or like "goat." The team diluted each carboxylic acid several times to assess how intensely each one contributed to BO in both groups. The carboxylic acids from teens' armpits retained their scents after more dilutions than did those from young children, suggesting the chemicals might be secreted in higher concentrations after puberty.

The teen BO also harbored two steroids that were absent from the young kids' samples. One smelled like sandalwood, a common fragrance in perfumes. The other smelled like sweat and urinals — parfum de locker room, if you will.

Changes in people's BO between infancy and puberty may be linked to alterations in their skin, including hormonal changes; a shift in its lipid, or fat, makeup; differences in the skin microbiome; or the activation of sweat glands and sebum glands, which exude an oily substance. However, it's still unclear which of these anatomical changes may explain the differences in this study.

Related: Humans can 'smell' each other's emotions — but we don't know how

In studying the participants' self-made body odorants, "we were very careful in considering all kinds of potential contamination," Loos said. They asked the infants' parents and the teens to avoid smelly foods containing spices, onions or garlic, and they provided perfume-free shower gels and unscented detergents. Nonetheless, many odorants picked up in BO samples were also detected in these provided supplies, so it's unclear how much they influenced the findings.

Conscious that odorants in the air might absorb into the cotton pads, the researchers also provided each participant with a second T-shirt to leave in the room, unworn. Most of the 42 odorants were also found in these unworn tees, but it's unclear whether they emanated off the participants or came from another source.

Some chemicals previously linked to BO went undetected in this study, including acetic acid, which gives vinegar its signature scent. This may be explained by the team studying a small, non-diverse cohort, or the fact that techniques differ in their ability to detect different substances.

Loos and colleagues plan to employ other approaches to capture a wider variety of odorants, as well as to explore how BO changes in other age groups, including older people. They also want to study more-intense BO, following exercise or multiple nights of sleep, for instance.

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!