Hormetic

Heat and cold, one honest tracker. Estimated dose from your real heart rate and water temperature. On device, no account, nothing sold.

Hormetic tracks how your body responds to heat and cold exposure, using heart rate and the temperature involved, with honest math and full transparency.

WHAT YOU GET

• Heart-rate tracking during a session, recorded as a standard HealthKit workout
• Heat: three color-coded zones (Zone 1, Zone 2, Zone 3) and an estimated heat-dose score from your heart rate, the temperature you enter, and session duration
• Cold (new): cold-plunge tracking with three calm zones — Entering, Moderate, Significant — and an estimated cold dose from your time in the water and the water temperature
• Contrast: do a sauna and then a plunge, and Hormetic notes the pattern with honest, recovery-framed context — never a combined-benefit claim
• Per-session detail: peak heart rate, time in each zone, calories, algorithm version
• Adapt: your weekly consistency, with estimated heat and cold dose as separate trends
• Full session history

HONEST BY DESIGN

• Every value the algorithm derives is labeled "Estimated"
• Heat and cold use separate, independently versioned algorithms; each session records the version that produced its values
• In cold, heart rate is shown for context but never scored — cold changes it in ways a wrist reading can't fairly judge
• Historical sessions are never silently recomputed
• Grounded in published research, with tappable source citations; cold-water safety and its risks are covered prominently in the app

PRIVATE BY ARCHITECTURE

Your data never leaves your device. No account. No analytics. No telemetry. No third-party SDKs. We do not sell personal information.

IMPORTANT

For heat, Hormetic does not require you to place your Apple Watch or iPhone in any hot environment — the temperature is a value you enter manually, and Apple Watch simply contributes heart rate from your wrist. A cold plunge is shallow-water immersion, which Apple Watch's water resistance supports, and cold-plunge water is within the watch's operating temperature range. On Apple Watch Ultra, submersion and water temperature are read by the watch's built-in sensor; on other models you enter the water temperature. Keep your devices within Apple's published guidelines — water resistance is not permanent, and depth limits apply.

Cold-water immersion carries real risk. The cold-shock response can cause gasping and raise heart rate and blood pressure — enter gradually, never breath-hold beforehand, and don't plunge alone. Hormetic is not a medical device and does not diagnose, treat, or prevent any condition. Consult a healthcare professional before starting heat or cold exposure, especially with a heart condition, high blood pressure, or pregnancy.

REQUIREMENTS

iPhone running iOS 18 or later. Apple Watch optional, used for heart rate; Apple Watch Ultra adds automatic submersion detection and water-temperature sensing for cold plunges.