In many species, female body odors reflect their reproductive status, and odors around the time of ovulation attract males, resulting in behavioral and/or physiological changes. In humans, several studies have suggested that female body odor signals periods of high fertility. For instance, vaginal secretions collected during the preovulatory and ovulatory phases are rated as more pleasant than those from the menstrual, early luteal, or late luteal phases. Additionally, axillary, armpit odors during the fertile phase are perceived by men as more pleasant, sexy, or attractive compared to those during the menstrual and luteal phases. Another study indicated that high-fertility scents collected from the armpit were chosen as more attractive than low-fertility scents. The fact that hormonal contraception results in the loss of these effects suggests that attractiveness is dependent on female hormones. It has been suggested that women’s behavior and physical attractiveness may serve as identifiable cues to fertility, and that men’s preferences are likely to increase for physical cues associated with high estrogen levels.
Changes in axillary volatile compounds within the menstrual cycle may be attributed to fluctuations in hormone concentrations, including estradiol and progesterone, within the cycle. In particular, estradiol receptors are expressed in many tissues and are believed to be involved in systemic metabolism and sweat gland secretory activity. Studies have revealed that amino acids and their derivatives in blood tend to increase during the menstrual phase and decrease during the luteal phase, whereas phospholipids and other substances in blood increase during the follicular phase, the first half of the menstrual cycle, and decrease during the luteal phase the second 14 days of the menstrual cycle. In a recent study the authors demonstrated that long-chain fatty acids, including tetradecanoic acid and (Z)-9-hexadecenoic acid, increase from the follicular phase to around ovulation and decrease during the luteal phase. This possibly reflects the degradation of blood-derived lipids on the skin surface, which increase during the follicular phase. Moreover, several compounds also increased during the follicular phase, and some of these tended to further increase during ovulation, suggesting the strong effects of estradiol on the variability of amounts of each compound during the menstrual cycle.
Researchers have identified three Ovulation-phase-increasing compounds namely: (1) (E)-geranylacetone: it is produced by oxidation of squalene and emits a floral or green odor quality and is among the prominently recognized substances in humans. (2) Tetradecanoic acid: it has an oxidized sebum odor quality and is detected in skin, saliva, breast milk, and amniotic fluid. Its primary production pathway is believed to be triglyceride hydrolysis by skin bacteria lipase or it may be derived from blood owing to its ubiquitous presence in cells and plasma. Human amniotic fluid and breast milk contain this odorant to which newborns exhibit a suckling response. (3) (Z)-9-hexadecenoic acid: commonly termed palmitoleic acid, it is nearly odorless. It is derived from palmitic acid and is presumed to be a precursor to (E)-2-nonenal, a compound representative of the odor of aging “aging odor,” which is generated through its breakdown by skin bacteria
Odor from the three Ovulation-phase-increasing compounds induces a sense of comfort and relaxation in men. Furthermore, when the odor of the basal axillary odor was combined with the three Ovulation-phase increasing compounds, it not only enhanced the attractiveness of low-attractive-level female faces but also suppressed the increase in salivary amylase, an indicator of stress-related bad odor, in comparison to the odor of the basal axillary scent alone. It has been reported that pleasant essential oil (like rose), enhance facial attractiveness, but it is noteworthy that such effects may also be present in components of body odor that fluctuate with the menstrual cycle.
In addition to body odor, several reports indicate various physical changes in women during the menstrual cycle. The voice during the ovulation period is perceived as the most attractive to men, and it has been demonstrated that the frequency of the voice also increases during the fertile phase. Photographs of a female face during the ovulation phase are perceived as more desirable than other times The redness of the face has been reported to decrease after the first day of menstruation and increases toward ovulation, although it is not detectable by the naked eye. It appears that physical features that enhance appeal to the opposite sex are heightened during the ovulation phase.
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