The agent isn't a chemical. It's the heat. Above 65°C the squamous cells lining your esophagus start to die, and a swallow cools by only a few degrees on the way down ¹. One scald heals in days; the damage is the repetition. Chronic injury means constant repair, repair means more cell divisions, and each division is another chance for a mutation to stick ².

The signal shows up wherever it's studied. In a 50,000-person Iranian cohort, tea at 60°C or hotter carried nearly double the risk, and sipping within two minutes of pouring ran about five times the risk of waiting four ³, ⁴. South American mate, drunk near boiling, roughly doubled it; cold mate showed nothing ⁵. A global meta-analysis put the hottest category at relative risk near 1.6 ⁶. Different drinks, one temperature signal.

Two people should care most. In a 456,000-person Chinese cohort, hot tea alone showed no independent signal, but paired with daily alcohol the risk ran five times baseline, and with smoking twice ⁷. Heat is less a stand-alone carcinogen than an amplifier. So if you smoke, drink heavily, or already carry elevated esophageal risk, temperature is one input you remove for free. For everyone else the absolute risk is small: fewer than five cases per 100,000 a year in the West. But the disease is brutal, with five-year survival near 20% ⁸.

Aim for a first sip under 60°C, the point where most people stop calling a drink hot and start calling it warm.

What you get is a probability, not a feeling. Nothing changes in a week, a month, or a year, and nobody tells you that you look healthier for cooling your coffee. The payoff is a thing that doesn't happen, decades out — like a seat belt, no felt benefit on any given day. The one exception is scalding-sippers with years of low-grade throat soreness, which fades within days.