Somewhere between the gym-maxxing and the sleep-maxxing, men started doing something genuinely useful: paying attention to their fertility. Searches for how to improve sperm quality have risen by more than 5,000%. Male fertility took centre stage at the ESHRE conference for the first time in 2026. On TikTok, men trade protocols the way they once traded lifting splits.
Some of it is grounded in decades of published research. Some of it will do nothing. A small amount of it can hurt you. Here is the split, plainly.
What spermmaxxing actually involves
The protocols vary, but the common ingredients are consistent: cold exposure of some kind, a large supplement stack, dietary changes such as four to six eggs a day, and a change of underwear. Some men abandon underwear entirely. Others put ice packs against the crotch in a sauna, sit in ice baths weekly, or dip in ice water directly.
The instinct behind most of it is correct. The execution is where it falls apart.
What the research supports
Reducing heat
This is the strongest part of the trend, and the oldest science in it. Your testicles sit outside the body for a reason: sperm production works best a few degrees below core temperature. A laptop on the lap has been measured raising scrotal temperature by up to 2.6°C. Regular sauna use has been shown to reduce sperm count and motility, with measures returning to baseline months after stopping. Hot tubs show the same pattern, and stopping reversed it in close to half of the men in one small study.
Heat is the one input in this whole conversation that is genuinely within your control, every single day.
Getting out of synthetic fabric
Also well supported, and often mangled online. Men frequently claim polyester is an endocrine disruptor that tanks testosterone. That specific claim is not established. What is established is older and simpler: in published work, men who wore polyester around the scrotum saw sperm counts fall dramatically, and recover after they stopped. Cotton and wool did not produce the same effect.
A Harvard study of 656 men found those who mostly wore boxers had 25% higher sperm concentration and 33% more motile sperm than men in tighter styles. Looser, natural, cooler. That is the whole finding.
Working to the 74-day clock
Sperm takes roughly 74 days to produce, plus around two weeks in transit. Nothing you do today shows up in a test tomorrow. Anyone promising fast results is selling something. Give any change three months before you judge it.
What the research does not support
Ice baths and cold plunges
Cold plunging is the centrepiece of most spermmaxxing content, and the evidence is thin. There is no meaningful body of research showing that extreme cold exposure improves sperm health, and some studies suggest heavy cold exposure may actually lower testosterone. Being cold all over is not the same as keeping one specific area in its normal range.
Ice directly on skin
Dipping in ice water or pressing ice packs against bare skin is the most common piece of practical advice online, and the one most likely to cause harm. Skin there is thin. Direct freezing contact risks cold injury and numbness, and there is no evidence that a short blast of extreme cold does anything useful for sperm production. Gentle and sustained beats brief and extreme, every time.
Testicle tanning
Promoted by a handful of influencers, warned against by clinicians. Exposure of that area to UV may reduce sperm counts and raises concerns about tumour risk. There is no upside worth this.
Going commando
Understandable logic, limited benefit. The problem is not underwear itself, it is tight, synthetic underwear that traps heat. Loose natural fibre solves the same problem without the practical difficulties.
The honest version of the protocol
If you strip out everything unproven, what remains is unglamorous and well evidenced:
- Keep laptops off your lap. Use a desk or a tray.
- Cut long saunas and hot baths while you are actively trying.
- Break up long periods of sitting.
- Wear loose, natural-fibre underwear rather than tight synthetics.
- Never put anything frozen straight against skin. Keep fabric in between.
- Give it three months before you expect to see anything.
- Get a semen analysis rather than guessing.
That is it. No supplement stack required. No ice bath. The parts of spermmaxxing that work are the parts nobody makes videos about, because managing your daily heat exposure is not dramatic enough for the algorithm.
Where NUMBNUTS fits
We built NUMBNUTS because we watched men do the sensible thing in the least sensible way: bags of frozen peas, gel packs against bare skin, ice cubes in a sauna. The instinct was right. The method risked a cold burn and never lasted more than ten minutes.
A natural-fibre boxer removes the plastic. A cooling insert held in a fabric sleeve, never against bare skin, handles the heat. That is the engineered version of what men are already trying to do with kitchen equipment.
NUMBNUTS is a comfort product, not a medical device. It is not a fertility treatment and we make no claims about results. If you are worried about your fertility, see a doctor and get tested. But if you are going to try to keep cool anyway, do it in a way that will not burn you.