Axillary steroids are produced by the testes, ovaries, apocrine glands, and adrenal glands. These chemicals are not biologically active until puberty when sex steroids influence their activity. The change in activity during puberty suggest that humans may communicate through odors. Several axillary steroids have been described as possible human pheromones: androstadienol, androstadienone, androstenol, androstenone, and androsterone.
* Androstenol is the putative female pheromone. In a 1978 study by Kirk-Smith, people wearing surgical masks treated with androstenol or untreated were shown pictures of people, animals and buildings and asked to rate the pictures on attractiveness. Individuals with their masks treated with androstenol rated their photographs as being "warmer" and "more friendly". The best-known case study involves the synchronization of menstrual cycles among women based on unconscious odor cues, the McClintock effect, named after the primary investigator, Martha McClintock, of the University of Chicago. A group of women were exposed to a whiff of perspiration from other women. Depending on the time in the month the sweat was collected (before, during, or after ovulation) there was an association with the recipient woman's menstrual cycle to speed up or slow down. The 1971 study proposed two types of pheromone involved: "One, produced prior to ovulation, shortens the ovarian cycle; and the second, produced just at ovulation, lengthens the cycle". However, recent studies and reviews of the methodology have called the validity of her results and existence of menstrual synchronization into question.
* Androstenone is postulated to be secreted only by males as an attractant for women, and thought to be a positive effector for their mood. It seems to have different effects on women, depending on where a female is in her menstrual cycle, with the highest sensitivity to it during ovulation.  In 1983, study participants exposed to androstenone were shown to undergo changes in skin conductance. Androstenone has been found to be perceived as more pleasant to women during their time of ovulation.
* Androstadienone seems to affect the limbic system and causes a positive reaction in women, improving mood. Responses to androstadienone depend on the individual and the environment they are in. Androstadienone negatively influences the perception of pain in women. Women tend to react positively after androstadienone presentation, while men react more negatively. In an experiment by Hummer and McClintock, androstadienone or a control odor was put on the upper lips of fifty males and females and they were tested for four effects of the pheromone: 1) automatic attention towards positive and negative facial expressions, 2) the strength of cognitive and emotional information as distractors in a simple reaction time task, 3) relative attention to social and nonsocial stimuli (i.e. neutral faces), and 4) mood and attentiveness in the absence of social interaction. Those treated with androstadienone drew more attention to towards emotional facial expressions and emotional words but no increased attention to neutral faces. These data suggest that androstadienone may increase attention to emotional information causing the individual to feel more focused. It is thought that androstadienone modulates on how the mind attends and processes information.
While it may be expected on evolutionary grounds that humans have pheromones, these three molecules have yet to be rigorously proven to act as such. Research in this field has suffered from small sample sizes, publication bias, false positives, and poor methodology.