McClintock discovers two odorless chemical signals influence mood

University researchers have discovered that two naturally occurring steroids produce odorless chemical signals that can improve the mood of women but have the opposite effect on men.

The discovery could lead to the establishment of a new category of odorless agents––modulator chemical signals––said Martha McClintock, the David Lee Shillinglaw Distinguished Service Professor in Psychology. McClintock is a leading expert on the relationship between mind, behavior and the functioning of the neural and endocrine systems.

Although the steroids probably do not trigger specific, predictable actions, “they are nonetheless psychologically potent,” McClintock writes in a paper co-authored with Suma Jacob, a University researcher. The paper, “Psychological State and Mood Effects of Steroidal Chemosignals in Women and Men,” is published in the current issue of Hormones and Behavior. McClintock and Jacob said the steroids should be studied further to learn more about their effects on humans and to determine if similar agents are part of the communication systems of other species.

For their study, McClintock and Jacob tested women’s and men’s responses to two steroids produced by the human body and often used in perfumes and colognes: androstadienone, which is produced by men, and estratetraene, which is produced by women.

In their first experiment, McClintock and Jacob tested 10 men and 10 women by applying a tiny amount of each steroid (2.4 millionths of a gram), diluted in propylene glycol, under their noses and on a spot on their necks. They also tested their study participants by applying only propylene glycol to the same areas.

The two researchers told the participants that they were studying odorants, including compounds added to perfumes.

McClintock and Jacob conducted a series of standard psychological tests to compare how the thoughts and moods of the study participants were influenced by exposure to the steroids and propylene glycol vs. exposure to the propylene glycol by itself. They found that women had a higher positive-stimulated response to both steroids, compared with exposure only to propylene glycol. Men reported lower levels of positive-stimulated response to both steroids, compared to exposure to only propylene glycol.

Because a few of the test subjects reported being able to smell something in the propylene glycol containing the steroids, the researchers decided to do a second series of tests to eliminate any possibility that subjects were responding to solutions because of smell. They decided to test women to see if the positive mood effects would be replicated.

For the second experiment, they added clove oil, a pleasant-smelling substance not commonly used in perfumes, to the propylene glycol to mask any possible odor of androstadienone, the steroid they used in this set of tests. They applied the solutions with the same tiny amount of the steroid under the women’s noses and on their necks. In a separate portion of the experiment, they also applied the solution without the steroid to the same areas.

McClintock and Jacob told the women they were studying changes in olfactory perception and psychological response within the menstrual cycle. Subjects were given a series of psychological tests over a period of two hours.

“Even though subjects did not identify or describe smelling androstadienone, the steroid had a significant effect on general mood,” Jacob said.

At the beginning of the experiment, the female participants all reported having a positive mood. “During the tedious two-hour study protocol, when they were exposed to clove oil, women’s moods deteriorated. Androstadienone, however, both maintained their initial levels of positive mood and prevented the increase in negative mood, which occurred when they were exposed only to clove oil and propylene gylcol,” Jacob explained.

Although androstadienone clearly had an effect on the women’s moods, the steroid would probably not trigger specific behaviors, which would be characteristic of compounds known as pheromones, McClintock said. Human behavior is influenced by a wide range of stimuli as well as learned societal restraints, she added.

McClintock established the first proof of human pheromones in a paper published in March 1998. She found that the compounds, undetectable as odors, play a role in the timing of ovulation.

Marketers of perfumes and colognes have made claims that the two steroids used in McClintock and Jacob’s tests are pheromones that serve as sexual prompts for men and women, androstadienone encouraging women to become interested in sex and estratetraene having a similar effect on men. The new research shows that these steroids do not produce specific behavioral responses.