A long list of companies and perfume products claim to sell desire through human pheromones this Valentine’s Day. But buyer beware. One of the chief pheromones in consumer products, androstenone, has a powerful effect on pigs, but no proven effect on humans, says Charles J. Wysocki, an olfactory neuroscientist at the Monell Chemical Senses Center. It is a pig pheromone, found in the animal’s saliva.

“There’s absolutely no scientific literature that shows that androstenone or the related steroid, androstadienone is the ‘magic bullet’ for use as a human pheromone,” Wysocki said.

Pheromones are chemical compounds secreted by animals that trigger behavioral responses, sometimes signaling reproductive readiness, fear or other emotions. While they’ve been observed for 55 years, no one knows exactly makes up these chemical compounds in humans, said George Preti, an organic chemist who works with Wysocki at Monell.

And in humans, Wysocki said, they’ve been overhyped as “sex attractants.”

Pheromones do trigger endocrine changes, such as increased testosterone. They are also responsible for famously syncing the menstrual cycles of women who live together. But there’s no evidence that human pheromone will actually attract a person of the opposite sex, as it does for moths and other animals

“(Pheromones’) effects are powerful but subtle. You don’t need much to cause the effect,” Preti said. Imagine, he said, the rankest underarm odor from the guy sitting next to you on the bus. No matter how overwhelming the smell, your nose is only picking up some parts per billion of a pheromone compound.

From the experts, here’s what your nose knows about pheromones, and what they can and can’t do for you:

1) Pheromones help create your “odor print.”

Many nonhuman animals get their pheromone-detecting power from an organ called the vomeronasal organ, or the VNO. In humans, that organ isn’t functional, Wysocki said, yet we still experience pheromones’ effects. It’s likely that body odors carry these chemical compounds through the air and our nose senses them, Wysocki said.

Pheromones help make up our “odor print,” he said. In addition to triggering biological and behavioral responses, they also deliver information. It seems our scents can tell others our age, sex, and even reproductive availability.

2) There is no human sex pheromone — that we know of.

A long line of pheromone-laden perfumes and colognes advertise that they will make you irresistible. Don’t buy it, Wysocki said. While there are pheromones in the animal world that will elicit a sexual response, there is no known human sex pheromone to date that will make you lucky. That doesn’t mean that they don’t exist, he added, but no one’s found them yet.

3) Pheromones will move babies towards their mothers.

One demonstrated pheromonal effect is found in newborn babies. A lactating mother produces a pheromone that attracts her child to her. For example, studies have found that breastfeeding infants will move toward breast pads worn by their mothers.

“Babies learn the odor of mother and food source very early on,” Preti said.

4) Pheromones enable humans to “smell fear.”

In 2008, researchers at Stony Brook University taped absorbent pads to the armpits of volunteers about to skydive for the first time. Then they had a second group of volunteers smell the sweaty pads while observing their brains with a scanner. The fear regions of the volunteers’ brains lit up when they got a whiff of the skydiving sweat, but not when they smelled normal sweat.

“The smell of fear begets fear,” Wysocki said.

5) Women’s smelly T-shirts can increase mens’ testosterone levels and make them act stupid.

In another study, men sniffed a series of womens’ T-shirts. Researchers found that the female odor raised men’s testosterone levels. It also increased their risk-taking behavior, Wysocki said.

6) The smell of a man’s armpits can be relaxing.

Researchers believe we release odors that contain pheromones from many different areas of our body, including armpits, back sweat and earwax. But men’s armpits are particularly potent. When women smelled odor from mens’ armpits, they reported feeling less tense and more relaxed, Wysocki said. That odor can also trigger changes in women’s menstrual cycles, Preti added.

In conclusion, raise your arms when you give your Valentine a gift today, Wysocki said. And until scientists can tease out the chemical compounds that trigger these responses, don’t trust the pheromone perfumes.