The effect pregnancy has on your sense of taste is well known (pickles and ice cream, anyone?), but the effect it can have on your sense of smell is less often discussed—and just as real. I learned the hard way about those changes in the olfactory system during pregnancy. As a beauty editor, I carry an extensive incense cabinet, and every smell made me sick during my first trimester. Even my favorite scent, Vanilla Powder by Matiere Premiere, made my stomach turn. I knew that pregnancy, with all its hormonal fluctuations, would bring an onslaught of uncomfortable symptoms, but I didn’t expect any of them to completely rehabilitate my nose.
It turns out I wasn’t alone in this experience. Anate Brauer, MD, a board-certified reproductive endocrinologist, says that the change in the way I perceived smell during this time is consistent with the experiences of other patients. Pregnancy isn’t the only time this change can happen, either; any subtle hormonal changes you experience—throughout your menstrual cycle, during menopause, and when you’re using hormonal birth control—can affect how you smell.
Previously, experts distinguished how hormonal changes and different stages in a woman’s life can affect the sense of smell.
Pregnancy
Caused by hormonal changes during pregnancy, changes in your sense of smell “usually happen in the first trimester,” says Dr. There is an evolutionary explanation, she explains: “When you’re pregnant, your body stays awake to protect you and your baby.” For some, that means nausea caused by everyday smells; for others, this biological response means that long-held odor preferences are changed overnight.
There is also an endocrinological explanation that the greatest increase in hormones during pregnancy occurs in these first weeks. Human chorionic gonadotropin (hCG)—the main pregnancy hormone responsible for fetal growth—peaks at about 8 to 11 weeks of pregnancy. These drastic hormonal changes can shock many systems in your body, including the olfactory system. But hCG is not the only hormone responsible, estrogen and progesterone are also involved.
Estrogen
The endocrine system has a lot more to do with your sense of smell than most people realize, and estrogen is the main hormone to blame if yours changes dramatically, says Dr. Brewer. Estrogen, which is important in regulating a woman’s reproductive system, fluctuates during pregnancy, puberty, throughout the menstrual cycle, and menopause. It is the hormone responsible for breast development during puberty, the growth of the lining of the uterus, and the formation of the fallopian tubes. “There are estrogen receptors throughout the central nervous system,” commented Dr. Bauer, and they start as soon as your hormones jump.
To explain how estrogen affects smell, Dr. Brauer zooms in: The olfactory system—from the lining of your nose to the brain’s smell processing centers—is dotted with these receptors. When estrogen levels rise, the smell may register as more intense. Sometimes that intensity reads like fun, like when you ovulate (we’ll get into that soon); sometimes, however, it can be overwhelming, which is how I felt when I was rummaging through my fragrance collection, desperate to find anything that wouldn’t make me want to throw up.
human chorionic gonadotropin (hCG)
For people who are pregnant, another hormone enters the mix: The aforementioned human chorionic gonadotropin, or hCG, is the hormone that indicates pregnancy when you take a home test. Produced by the placenta, hCG supports the development of the baby by signaling the body to maintain the pregnancy and suppress the hormones that cause menstruation. It also helps to strengthen the immune system, ensuring that the mother’s body does not reject the fetus.
“There are hCG receptors in your central nervous system, too, which can increase the sensation of nausea,” says Dr. Brewer. Nausea itself can increase aversion, turning once-loved sensory notes into immediate stimuli. I felt very recognized when he told me this; even the delicate au de toilettes in my fragrance cabinet made me sick.