The Big Picture
The three passages here all come from Huberman Lab, with Andrew Huberman explaining the material himself, so this brief is one host's view seen from three angles: sexual development, smell and chemical signaling, and attraction [1][2][3]. He starts from a definition. A hormone is a chemical released in one part of the body, usually from a gland, that travels and acts on tissues elsewhere, unlike neurotransmitters, which act locally [2]. Steroid hormones, he explains, act quickly on cells and slowly through gene expression [2].
From there the passages follow hormones into behavior. In development, DHT builds male genitalia in the womb and testosterone drives the changes of puberty, while estrogen, converted from testosterone by aromatase, masculinizes the brain, which the episode calls a surprising fact [2]. In adult life, the passages describe how menstrual cycle phase changes how people smell to each other and how well women discriminate odors [1][3], and how much of our evaluation of other people runs through chemicals we are not aware of [1]. The episode on love also covers hormones, dopamine and libido, and Helen Fisher's dopamine, serotonin, testosterone and estrogen types [3].
Where the Experts Agree
- The menstrual cycle changes smell-related behavior. Huberman cites a 2009 review by Doty and Cameron in Physiology and Behavior showing that women generally outperform men in odor discrimination and that this varies across the menstrual cycle [1]. In the episode on love he describes two studies: men rated the odor of T-shirts worn by women as most attractive when the women were in the pre-ovulatory phase, and women in the pre-ovulatory phase rated men's odors as more attractive, especially those of more physically symmetrical men [3].
- Much of this happens below awareness. Women in stable relationships can pick their partner's T-shirt out of about a hundred at better than chance, even when the scent is diluted below conscious detection [1]. In a Weizmann Institute study he calls his favorite example, people almost always touch their eyes or face within seconds of shaking hands with a stranger, even after the person has left the room, transferring chemicals from the handshake to a mucous membrane [1].
- Hormones depend on the machinery that receives them. Androgen insensitivity syndrome is his example of why hormones only work if their receptors do [2].
- Outside factors can interfere. Oral contraception eliminated both of the cycle-related odor effects in the attraction studies [3]. The episode on sexual development lists evening primrose oil, atrazine, cannabis, alcohol and cell phones as environmental influences, and is described as covering how cannabis, alcohol, herbicides and phones may alter the hormones and receptors that shape development [2].
- Humans are still animals in this respect. Huberman compares the handshake finding to bunting, when dogs and cats rub their scent glands on us, and says, "Now that might seem odd or even gross to you, but I think it's beautiful" because it shows how much we still share with other animals in evaluating our chemical world [1].
Where They Differ
With a single host behind all three passages, there is no disagreement to report; the differences are of emphasis [1][2][3].
- Development versus the present moment. The sexual development episode is about what hormones build over time: genitalia in the womb, the changes of puberty, the masculinizing of the brain, and topics such as finger-length ratios, prenatal hormones and sexual orientation [2]. The other two are about effects that shift with the phase of the menstrual cycle or happen within seconds of a handshake [1][3].
- Hormones versus other chemicals. The smell episode is framed around pheromone-like chemicals that people use to affect each other, not hormones as he defines them [1][2]. The love episode puts hormones beside other influences on desire and bonding: childhood attachment, the autonomic nervous system, which he pictures as a "seesaw" that caregivers and partners help tune, empathy and positive delusion [3].
- Explanation versus tools. The sexual development episode moves from textbook endocrinology to rare natural experiments and then to everyday tools [2], while the love episode also takes in studies on maca, tongkat ali and tribulus [3].
Practical Takeaways
- Keep the four levels of sex apart when you think about hormones: chromosomal, gonadal, hormonal and morphological [2].
- Remember that a hormone level is only half the story; hormones only work if their receptors do [2].
- Know that attraction runs deeper than looks: odor, menstrual cycle phase and oral contraception all shifted perceived attractiveness in the studies Huberman describes [3].
- If you use oral contraception, be aware that it eliminated the cycle-related odor effects in those studies [3].
- Be aware of the environmental influences the sexual development episode flags: evening primrose oil, atrazine, cannabis, alcohol and cell phones [2].
- Inhale through the nose when you want to be alert: Huberman says it wakes the brain up and supports learning [1].
- Take a few deliberate sniffs to sharpen smell and taste, and note that smell can reflect brain health and recovery [1].
Sources
- How Smell, Taste & Pheromone-Like Chemicals Control You · Huberman Lab
- How Hormones Shape Sexual Development of the Brain and Body · Huberman Lab
- The Science of Love, Desire, and Attachment · Huberman Lab
