Cold Packs, Hot Saunas, and the Quest for Super‑Charged Sperm

When you hear someone talk about “icing the balls,” you probably picture a prank, not a serious fertility hack. Yet a growing corner of the biohacking world is treating scrotal cooling like the next big nootropic, convinced it will turn ordinary sperm into Olympic‑level swimmers.

Enter Bryan Johnson, the tech billionaire behind Project Blueprint. Johnson’s daily regimen is something out of a sci‑fi wellness manual: 27 sauna sessions a week, a strict 2,000‑calorie diet, and—most eye‑catching—a frozen gel pack strapped to his groin for fifteen minutes at a time. He proudly posted his own numbers on X, claiming a 57 % jump in total motile sperm count, a 26 % rise in concentration, and a four‑fold increase over the “average” male.

Johnson isn’t the only one. On Reddit’s biohacking subforums—where more than half a million visitors congregate each week—users share similar protocols. One self‑described “testicular‑ice enthusiast” wrote, “Ice pack over my boxers, 15 minutes, three to four times a day.” After a year, he boasted the highest testosterone reading he’d ever seen, “more powerful ejaculations,” and a libido that was “through the roof.”

So, is there any scientific grounding for the practice, or is it just another wellness fad? The basic premise isn’t entirely fanciful. Human testicles sit outside the body because sperm production works best a few degrees cooler than core temperature—about 95 °F (35 °C). A 2005 study found that for every 1 °F rise in scrotal temperature, sperm concentration dropped roughly 40 %. Another trial showed that nightly scrotal cooling for 8–12 weeks improved both sperm concentration and total count.

But there’s a crucial nuance: those studies used gentle, wearable cooling devices worn overnight, not the aggressive, intermittent ice‑pack method Johnson touts. Dr. Ramy Abou Ghayda, a urologist and chief medical officer at Legacy, notes that while heat can indeed damage sperm, deliberately plunging the testes below their optimal temperature hasn’t been proven safe or effective. Urologist Lye Diwa adds, “Small studies hint at benefits, but there are no large clinical trials endorsing ice packs as a fertility booster.” In fact, a separate investigation observed that acute cold exposure actually lowered testosterone in young men.

Martin Gross, an associate professor of surgery at Dartmouth, argues that the evidence for a direct link between scrotal icing and improved testosterone or sperm quality is virtually nonexistent. He points to lifestyle factors—adequate sleep, regular exercise, a healthy weight, and moderating alcohol—as far more reliable ways to support male reproductive health.

It’s worth noting that male testosterone levels have reportedly fallen about 54 % between 1972 and 2019, a trend attributed to environmental stressors like heat, endocrine‑disrupting chemicals, and microplastics—issues Johnson himself has loudly campaigned against. The anxiety many men feel about declining fertility is understandable, and the appeal of a simple, low‑cost “cold pack” fix is strong.

Bottom line? While keeping the testes cool is a legitimate component of fertility care, slapping an ice pack on them multiple times a day is a leap beyond what current research supports. If you’re curious, the safest approach is to aim for modest temperature reduction—think breathable underwear, avoiding hot tubs, and perhaps a cool night‑time garment—while also focusing on sleep, diet, and exercise. The ice‑pack craze may be more of a cultural moment than a medical breakthrough, at least for now.