Breast Thermal Patterning in Response to Reproductive Hormones and Exercise

Abstract

Abstract. Thermography of the breast offers noninvasive insight into vascular and metabolic activity, yet data on the influence of reproductive hormones and exercise on surface temperature remain limited. A longitudinal study of five healthy, regularly menstruating women was conducted over one complete cycle (∼30 days), measuring daily first-morning urine for estrone-3-glucuronide (E3G), pregnanediol-3-glucuronide (PdG), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) via Mira fertility kits. Resting breast temperature was captured biweekly using infrared (IR) imaging and nine skin-mounted thermistors at standardized positions. Weekly exercise sessions entailed 20 min at 80–90% age-predicted maximal heart rate, with thermal recordings taken every 30 s for 10 min postexercise. Resting temperature varied significantly across cycle phases, with progesterone (PdG) emerging as the strongest hormonal predictor, although mixed-effects models indicated that individual baselines dominated. Exercise unexpectedly induced a small but consistent surface cooling that resolved within approximately 10 min. Hormone-based models poorly predicted postexercise thermal changes, underscoring the transient nature of thermoregulatory responses. These results delineate distinct hormonal and exercise-induced breast thermal signatures, highlight inter- and intra-individual variability, and inform the personalized calibration of wearable thermographic systems and the timing of clinical scans, particularly by accounting for progesterone-driven luteal warming and short-term cooling from exercise.