All the ladies in the house, have you ever wondered why there may be times when your menstrual cycle is in complete sync with your roommate, mother, sister, or potentially a friend that you spend so much time with? It can be merely a coincidence, but maybe that’s not the case every time. Let’s take a look at various research articles that talk about synced menstrual cycles and what might cause that sync, but before that, we can discuss the bigger picture of the menstrual cycle and the hormones involved.
Individuals of the same species often release airborne chemical signals – pheromones – in the environment which can affect the behaviors and physiology of others (Stern & McClintock 1998). An experiment on rats showed that there are two different types of pheromones that affect the length and synchrony of menstrual cycles at different times of the ovarian cycle. Rats are good experimental models for humans, which is why it can be predicted that humans might also have at least two different types of pheromones that might affect the ovarian cycle. In their study, Stern & McClintock (1998) tried to check if compounds from other individuals affect either the hormones or the lengths of menstrual cycles. In this experiment, they took odorless compounds (pheromones) from the armpits of women volunteers before and after ovulation. These axillary compounds were then “smelt” by the recipient women. Yes, it could be as gross as it sounds but luckily for the participants, they had no idea what the substance was, to avoid any bias.
Results showed that the pheromones collected before ovulation- in a phase known as the follicular phase of menstruation – accelerated the surge of the luteinizing hormone before ovulation; shortening their menstrual cycle. Luteinizing hormone (LH) is a hormone that can be measured to check for ovulation as it is generally elevated 34-36 hours before ovulation. On the other hand, the pheromones collected after ovulation, lead to a delayed surge in LH and lengthened menstrual cycles in the recipient women. Now how does any of this relate to the main idea of the article? Before we can dive deep into synced menses, it was vital to provide evidence for the existence of human pheromones. Now that we know, human pheromones do in fact lengthen or shorten menstrual cycles, let’s look into studies that found interesting results about synced menstrual cycles!
There has been a lot of data that show menstrual sync between women who live closely together in the family or spend a lot of time together. An experiment conducted by Jahanfar et al. (2007), included a group of 88 females who lived together in houses with five to eight rooms and were asked to keep a thorough track of their menstrual cycle. The results showed that out of 88 subjects, 52 females had synchronized menstrual cycles. From this particular study, they could conclude that the roommates, best friends, or both, presented menstrual synchrony at a rate of 50-60%. This may not seem like a lot but is still a pretty significant rate at which menstrual synchrony occurs. Researchers proposed that this rate could be due to the constant exposure of pheromones in close proximity to each other.
“There has been a lot of data that shows menstrual sync between women who live closely together in the family or spend a lot of time together”
Now that we’ve established how pheromones are exchanged between females, we can look at research showing the effects of male pheromones on females. Scientists from the University of Pennsylvania (Preti et al. 2003) found that male perspiration (pheromones in the form of sweat) can have significant physiological changes in women like brightening a woman’s mood, reducing tension, helping in relaxation, and having direct effects on the release of LH – a contributing factor for the length and time of menstruation. The subjects for this study included 18 women who had male axillary compounds applied on their upper lip and were asked to rate their mood after a few hours. To ensure that the male pheromones are not tampered with, male subjects were asked to bathe with fragrance-free soap and were told to avoid using deodorant or any other substance that would react with the natural male odor. The study had to be a blind study, where the female subjects were unaware of the substance applied to their upper lip. Most participants mentioned that they felt much less tense and more relaxed. Additionally, blood samples indicated an increase in LH. The scientists of this study mentioned that this was important to study because if male pheromones have such a profound effect on female mood as well as LH hormone secretion, then there is potential to artificially develop a “male odor” that can mimic male pheromones to effectively manipulate the effects they observed. That can certainly be a unique helpful tool for females who may be struggling with irregular menstrual cycles.
Menstrual synchrony has already been the subject of many research projects. However, if the relationship between synchrony and pheromones is correlational or causal is still a debate. The main reason behind it is mixed experimental results. There are experiments that support this theory but there are also studies that don’t have significant results to be able to conclude a causal relationship between them. What are your thoughts on this? Have you ever heard of menstrual synchrony and is it biological? Let us know in the comments below!
Jahanfar, S., Awang, C. H. C., Abd Rahman, R., Samsuddin, R. D., & See, C. P. (2007). Is 3α-androstenol pheromone related to menstrual synchrony?. BMJ Sexual & Reproductive Health, 33(2), 116-118.
Preti, G., Wysocki, C. J., Barnhart, K. T., Sondheimer, S. J., & Leyden, J. J. (2003). Male axillary extracts contain pheromones that affect pulsatile secretion of luteinizing hormone and mood in women recipients. Biology of reproduction, 68(6), 2107-2113.
Stern, K., & McClintock, M. K. (1998). Regulation of ovulation by human pheromones. Nature, 392(6672), 177-179.