Our sense of smell is important for our health and well-being. It helps us select wholesome food, heightens the appetite, and warns us of harmful or spoiled products. Our ability to perceive smells also helps us navigate the environment, warning us about dangers such as a gas leak, smoke and fire, or mildew in the walls. But our sense of smell gives us even more subtle and profound cues that influence our romantic relationships, social interactions, and attitudes towards other people.
Although for most of us, this information doesn't register at the conscious level, the human nose can detect even very faint scents in the environment. In fact, the partners we choose, the people we befriend, and whom we tend to avoid may be primarily determined by smell. In this article, we'll discuss the wonders of smell and how shifting hormones throughout the menstrual cycle, during pregnancy, and in perimenopause influence what we perceive through our noses.
Good and bad—all smells are important. Like any other sense, olfaction is crucial for our protection and how we engage with the world. In addition to helping us find nutritious food and avoid dangers, our ability to detect scent molecules influences our emotions, memories, and relationships.
So, how does olfactory perception work? Odours are chemical molecules light enough to travel through the air. Some smells are stronger and some fainter, but almost everything releases odorant molecules that, when inhaled, attach to specialised receptors located in the membrane that lines the nasal cavity. Humans have 5–6 million olfactory receptors that can detect around 400 different molecular scent patterns. These building blocks combine in countless ways to create different scent profiles. In the last decade, researchers have come to believe that humans can detect around one trillion smells—far more than the previously believed ten thousand. This may seem like a lot, but other mammals have a much keener sense of smell. For example, dogs are famous for their curious noses and can identify scents from several kilometres away, and elephants have more scent receptors than any other mammal.
Whenever we smell something, it is because we have inhaled molecules of a substance our olfactory receptors recognize. These receptors send information to the brain, so we can use it to make decisions. The olfactory bulb, the seat of these smell receptors, sits quite close to the hippocampus, the learning and memory center of the brain. We are still trying to figure out how these two centers interact, but it’s clear that smells can be powerful memory triggers. For example, the smell of a perfume your mother wore when you were little can bring up vivid memories of your childhood.
Pheromones are chemicals produced by our bodies to influence the behaviour of those around us. They act like hormones but affect other people. We release our pheromones into the air primarily through sweat, but they are also found in other bodily secretions. You can't see them—or even smell them—but they can stimulate attraction and sexual arousal and have a powerful effect on your choice of a romantic partner. Some people claim to be able to smell when someone feels turned on. Pheromones have been found in all animals studied. They play an important role in mate selection but are also involved in marking territory, raising alarm, acquiring food, and other social behaviours. Although humans have relatively weak olfactory powers, we are still affected by the world of smells.
We already know that certain scents affect us even if we can’t smell them, but you might wonder what the connection between your hormones and your olfactory senses is. Before we go any further, let's better understand how female hormones work during the menstrual cycle.
Typically, a healthy menstrual cycle spans 28–35 days (with a few outliers at each end). As hormone levels rise and fall over the course of these 4 to 5 weeks, your body goes through four distinct phases. The beginning of this cycle is defined as the first day of your period.
The short answer is yes. While your sense of smell doesn’t actually change, your sensitivity to odours might. This is called hyperosmia, and can happen for various reasons, including hormonal fluctuations. It doesn’t happen for all women, but many say they become more sensitive to certain smells as their cycle progresses.
Some women experience hyperosmia during ovulation, perhaps to ensure they are with a suitable mate during the fertility window. Many women report they can sense smells hardly noticeable to others during this time. Studies have shown that olfaction sensitivity during ovulation influences the choice of partner or, if we are already partnered, our level of attraction to that person. Studies observing the behaviour of heterosexual women throughout their cycles noted that their subjects were more attracted to traditionally masculine men during ovulation. However, this didn't hold true for long-term partners—men with more feminine characteristics or fatherly features had better success in lasting relationships. One explanation for this curious observation is that, from an evolutionary perspective, dominant genes and a strong protector are an advantage for a vulnerable pregnant woman, but once the baby is born, a more attentive and caring partner brings more benefits.
Some women say they lose their feeling of attraction for their partners during ovulation but regain it afterwards. This phenomenon can be attributed to a shift in how we perceive pheromones during fertile days. Men are also sensitive to this. Studies show that men can sense when women are ovulating. While they may not be consciously aware of what's happening, most heterosexual men will find a woman especially attractive when she's ovulating for the same reason women have a higher sex drive and find masculine men more attractive—to ensure reproductive success.
Olfactory sensitivity can shift again in the luteal phase. Some women report being more sensitive to bad smells—your partner's socks, old trash in the bin, or the neighbour's cooking. This may be linked to the body preparing for a potential pregnancy. Heightened sensitivity to bad smells might serve to protect a developing foetus from spoiled and dangerous foods.
Probably the most talked about change in olfactory perception happens during pregnancy, especially in the first trimester. One of the first signs of pregnancy is a heightened sense of smell. Some pregnant people report being able to notice smells from far away and can even tell what another person ate for lunch. It is common for expectant mothers to be disgusted by the smell of alcohol, tobacco smoke, raw fish and meats, eggs, and even perfumes and scents used in body care and cleaning products. Unsurprisingly, pregnancy hyperosmia can cause loss of appetite, nausea, and vomiting—nature's way of making extra sure the baby is safe from potentially harmful substances.
Perimenopause is the time of life when a woman’s body begins the transition to menopause. This typically starts in the early to mid-40s (but for some it can begin years earlier or later) and ends an average of four years later (but anything from 2 to 10 years is not uncommon) with menopause—when you have gone an entire year without a period.
Many people going through perimenopause report changes in their sense of smell and heightened sensitivity to certain odours. Changes in olfaction are linked to the precipitous drop in oestrogen that occurs at this time. Hormonal fluctuations may affect the brain centres responsible for processing odours causing some perimenopausal women to experience phantosmia—phantom smells or olfactory hallucination. This is why some perimenopausal women worry about how they smell or react strongly to other people’s body odour when no one else seems to be bothered.
While hormones can impact even the smallest details of our lives, sometimes increased olfactory sensitivity has to do with some medication you are using or an indication that there is something going on with your health. Conditions that can affect your sense of smell include:
It’s worthwhile to take a moment to reflect on the invisible world of smells now and then. Compared to many other animals, the nose is not our primary sense organ, but even so it can have a powerful influence on our safety, wellbeing, and social relationships.
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