A woman's mood and appetite are clearly tied to her menstrual cycle, but other, more subtle changes in thinking and behavior also occur. In particular, her sense of smell sharpens as fertility peaks in the latter half of her cycle.

A study published in March in Hormones and Behavior compared the smell sensitivity of 16 women taking oral contraceptives and 17 naturally cycling women during two different phases of the menstrual cycle—around the time of ovulation and during the luteal phase, immediately after ovulation. Participants sniffed odors of lemon, peppermint, rose, musk and the male pheromones androstenone and androsterone. Naturally cycling women near ovulation were more sensitive to musk and the pheromones than the women on contraceptives. The effect may not be limited to male scents: a study in March in Physiology and Behavior suggests that women have a sharpened sense of smell in general during their luteal phase, as measured by their ability to detect the subtle odor of the alcohol n-butanol.

These results are typical of research in this area; effect sizes are small, and not all studies agree on the details. Even so, the findings support a popular hypothesis that hormone levels in a woman's body influence her senses and preferences in a way that promotes reproduction.

“I believe these variations in olfactory sensitivity are closely tied to the functions of the reproductive system, where the capacity to identify certain odors increases at times when procreation is more likely,” says Jessica McNeil, a doctoral student in psychology at the University of Ottawa's School of Human Kinetics, who co-authored the Physiology and Behavior study.* She cautions, however, that some studies have found conflicting results. The physiological mechanisms that cause these effects also remain unclear, as her research has not found a relation between levels of specific hormones and olfactory sensitivity.

*Correction (10/22/13): This sentence was edited after posting to correct the name of the journal.