Jerilynn C. Prior BA, MD, FRCPC, Professor Emerita, Endocrinology/Medicine University of British Columbia
Breast self-knowledge sounds pretty weird, doesn’t it? And if I further say, I want to share about breast tenderness and swelling plus the size of the areola (the darker circle around the nipple), you are sure I’m ‘out to lunch’.
Why do we feel so peculiar about breast topics? Because breasts, like menstrual cycles, are unmentionable in Western culture. Yes, they are featured heavily in pornography and in some men’s imaginations, but we, women+ (of all genders) usually don’t think much about them.
So why bother you with breast information? First, because this myth and unmentionable stuff is meant to keep women ditzy and dependent. Second, because self-knowledge is empowering. In particular, understanding the changes and responses of breasts to estrogen and progesterone can help us understand our menstrual cycles and ovulation.
Over a decade ago, we at the Centre for Menstrual Cycle and Ovulation Research, set out to analyze the Menstrual Cycle Diary© and ovulation (Quantitative Basal Temperature© (QBT) information collected over about a year by 53 community-dwelling, healthy, non-smoking and amazingly committed women aged 20-41. These women (and a few others) made possible the iconic study published in the New England Journal of Medicine in 1990 that showed for the first time that normal progesterone (essential length of the luteal phase), not just normal estrogen (cycle lengths 21-36 days), was needed to prevent bone loss 1. As a group, we call these 53 women+ with an average of 13 cycles of Diary and QBT data, the Prospective Ovulation Cohort (POC) because all had to have two normally ovulatory as well as normal-length menstrual cycles to join our original study.
When she began her study of breast tenderness and swelling, Dr. Mary Wood, was a medical student. By the time she completed and had published her evaluation of these breast experiences by Diary and QBT data2, she was a resident training to become a specialist in Internal Medicine.
What did Mary learn about breast tenderness and swelling?
First, that a little breast tenderness and swelling were commonly recorded by these healthy women. We can therefore say that these experiences are expected and normal. After all, breasts have both estrogen and progesterone receptors and these hormone levels are normally high for parts of the menstrual cycle. But importantly, and against our hypothesis, was that more breast tenderness and swelling occurred in normally ovulatory cycles than in cycles with a little less estrogen and progesterone (regular lengths but short luteal phases). We had thought that higher progesterone levels would decrease estrogen’s breast tenderness-promoting effects.
When in the cycle were breast tenderness and swelling most likely? At the very end of the cycle and just before the period. Another very interesting thing is that breast tenderness and swelling increased together! See this figure from Dr. Wood’s paper:
Figure 1: Increases in breast tenderness and swelling in the late luteal phase of ovulatory cycles. All ovulatory cycles in 53 women are lined up on the day of ovulation (0). Breast tenderness (top panel) is scored 0-4 and breast swelling (bottom) is scored a 1-5 with “3” meaning “usual experience”.
What did we learn about the size of the breast’s areola?
When I was first working in the 1980s with transgender people in Vancouver General Hospital’s Gender Dysphoria Clinic, I saw a breast areolar change that taught me something 3. A transwoman came to this clinic with small but reasonable sized breasts with very small (man-sized) areola. She told me that she had previously gotten estrogen “off the street.” That said to me that estrogen makes the breasts swell but doesn’t enlarge the areola.
I prescribed her estrogen, the androgen-blocking medicine, spironolactone (to help reduce her heavy facial hair) and also prescribed the progestin (synthetic progesterone knock-off closest in action to progesterone) medroxyprogesterone because estrogen and progesterone are both important women’s hormones 4. Note—it was 1996 before we first had oral micronized progesterone available as a therapy in Canada. I later wrote a perspectives article describing why it is important for transwomen to have progesterone as well as estrogen treatment 5.
Over that first year of her official treatment, her breast areola increased from the size of a quarter coin (Tanner III) to as big as a loonie (Canadian one dollar coin, Tanner V). It seemed to me that taking the progestin caused her increased areolar size. Since then, I’ve always wanted to study areolar size.
It will help to know how breast changes as it is maturing (or growing up) are officially graded:
We started the Menstruation and Ovulation Study 2 (MOS2) in 2019, just before the first lock-down in the SARS-CoV-2 pandemic. We had added extra and optional studies into this single-cycle Diary and QBT study—including the investigation of breast areolar diameter for which 73 women+ (almost 60%) volunteered. Once restrictions were lifted, we began measuring each volunteer’s breast areola diameter (width) on each breast. This study was led by UBC medical student, Ally Baaske, whose abstract was presented at the Endocrine Society Conference in 2025 https://doi.org/10.1210/jendso/bvaf149.
What did Ally learn about healthy women’s breast areolar diameter?
Participants in MOS2 were regularly cycling, community women+ with a median age of 29 and BMI that was a healthy 24.5. Their average areolar diameter was a mature (Tanner V) 3.9 centimeters or 1.5 inches.
We had full ovulation information for 61 women of whom 45 were ovulatory and 16 anovulatory or didn’t release an egg and make progesterone that cycle (likely because of pandemic stress). Once the areolar size increased in the teen years (like the lengths of long bones), it would stay the same. So we looked at use of progestins and found that 70% had taken progestin-containing combined hormonal contraception (the Pill or CHC). Less than 10% had delivered a child thus we could not relate these MOS2 data to a potential role of progesterone to increase the size of the areola.
However, we discovered two other interesting things—the bigger the breast size (bra with cup D) and the greater the body size (weight, BMI or waist circumference), the larger the areola. We also learned that a given woman’s left areola was significantly larger than the right, much as the left breast is reported to be larger.
In summary, it is reassuring to learn that a little breast tenderness and some swelling are normal before menstruation. And appreciating that the darker part around the nipple increases in the teen years, likely after ovulation has been established and progesterone is released, and its usual size is close to 1.5 inches is interesting to know. (When you look at the nudes in classical museum paintings, what is their areolar size?)
We, as women, cannot take charge of our health and reproduction unless we have access to sufficient, and reliable information.
Reference List
- Prior JC, Vigna YM, Schechter MT, Burgess AE. Spinal bone loss and ovulatory disturbances. New Engl J Med 1990;323(18):1221-1227.
- Wood M, Shirin S, Goshtasebi A, Prior JC. Breast tenderness and swelling experiences related to menstrual cycles and ovulation in healthy premenopausal women: Secondary analysis of the 1-year “Prospective Ovulation Cohort”. PLoS One 2025;20(5):e0321205. DOI: 10.1371/journal.pone.0321205.
- Prior JC, Vigna YM, Watson D. Spironolactone with physiological female gonadal steroids in the presurgical therapy of male to female transexuals: a new observation. Archives Sexual Behavior 1989;18:49-57.
- Prior JC. Women’s Reproductive System as Balanced Estradiol and Progesterone Actions—a revolutionary, paradigm-shifting concept in women’s health. Drug Discovery Today: Disease Models 2020;32:31-40. DOI: https://doi.org/10.1016/j.ddmod.2020.11.005.
- Prior JC. Progesterone is Important for Transwomen’s Therapy-applying evidence for the benefits of progesterone in ciswomen. J Clin Endocrinol Metab 2019;104:1181–1186. DOI: 10.1210/jc.2018-01777.