Cold exposure & cold plunge

Scrotal cooling — strong evidence: Nocturnal scrotal cooling (~1°C reduction) significantly improves sperm concentration and total sperm count. It is one of the best-supported non-pharmacological male fertility interventions (Jung 2001). Practical options include cooling underwear and behavioral changes (avoiding tight clothing, laptop heat).

Whole-body cold plunge — nuanced: Repeated cold water immersion decreased serum testosterone and estradiol in young men (Pilch 2021). This is the opposite of what's claimed on social media. Targeted scrotal cooling works; whole-body cold exposure is a different intervention with different effects.

PCOS — exciting animal data: 20 days of cold exposure reversed PCOS in rats — restoring estrous cycles, reducing testosterone and LH, clearing cystic follicles, and improving insulin sensitivity. The mechanism was brown adipose tissue (BAT) activation improving glucose metabolism (Yuan 2021). BAT metabolism is lower in postmenopausal women and with ovarian suppression, suggesting estrogen-BAT interaction. No human fertility trial yet.

Menstrual pain: Whole-body cryotherapy (-110°C, 3 min sessions) significantly reduced menstrual pain and improved sleep quality in a 2025 RCT. Cold water swimmers also self-report positive effects on menstrual symptoms.

Cycle-phase note: Cold tolerance shifts across the cycle. The luteal phase's elevated core temperature means you shiver later and may tolerate cold better — but physiological responses differ from the follicular phase.