The physics caps the harm. Bluetooth runs at 2.4 GHz, the same band as your microwave and your router; the only thing that band can do to tissue at this power is warm it, and an earbud warms your ear by well under a tenth of a degree ¹. Regulators cap radio energy deposited in the head at 1.6 watts per kilogram ². Earbuds run a hundred to a thousand times under that.

The cancer question is about as settled as these things get. If Bluetooth caused cancer, phones would have shown it first, at hundreds of times the power. A prospective cohort of 264,574 adults across five countries found no association between phone use and brain tumours ³. A pooled review of sixty-three studies reached the same null with moderate certainty ⁴.

The scare traces to a 2011 "possibly carcinogenic" label ⁵, resting on a case-control study where heavy users had forty percent more glioma ⁶ — but that same study also showed ordinary users getting less glioma than non-users, the fingerprint of people misremembering their phone habits in interviews. The cohorts that followed found nothing ⁷. A vocal minority still argues the case isn't closed ⁸; the prospective data keeps moving one way.

Your hearing is what pays. Not your brain — the hair cells in your inner ear, which do not grow back. The damage is silent: unnoticed at twenty-five, blaming restaurants at thirty-five, asking people to repeat themselves at forty-five. The WHO puts 1.1 billion people aged twelve to thirty-five at risk right now, mostly from earbuds at commute volume ⁹. One in five US adults in their twenties already shows measurable damage on an audiogram ¹⁰, and none of them has noticed.

Two levers, and they are not equal. Volume first; wired-versus-wireless a distant second.