Hormetic

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: 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
• Spa (new): hot tubs and hot baths, with their own zones and an estimated soak dose from your time immersed and the water temperature. A separate algorithm from heat — a 40 °C soak is not a 90 °C sauna, and one score cannot honestly describe both
• Contrast: follow a sauna or a soak with 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, cold, and soak dose as separate trends
• Full session history

HONEST BY DESIGN

• Every value the algorithm derives is labeled "Estimated"
• Heat, cold, and spa use separate, independently versioned algorithms; each session records the version that produced its values
• In cold and spa, heart rate is shown for context but never scored — water changes it in ways a wrist reading can't fairly judge
• The soak estimate stops growing past 40 °C and past 20 minutes, because that is where the published evidence stops. More time is not more dose
• Historical sessions are never silently recomputed
• Grounded in published research, with tappable source citations; 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 — YOUR DEVICES

Hormetic never asks you to put a device anywhere Apple's own guidelines say it should not go.

For heat, Hormetic does not require you to place your Apple Watch or iPhone in any hot room — the temperature is a value you enter manually, and Apple Watch simply contributes heart rate from your wrist.

Cold plunges, hot tubs, and hot baths are shallow-water immersion, which Apple Watch's water resistance supports. Hormetic's own in-app guidance caps a soak at 40 °C (104 °F), well under the 55 °C (130 °F) figure Apple publishes for Apple Watch Ultra in a hot environment. As Apple recommends, rinse your Watch with fresh water after a treated pool or tub. 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.

IMPORTANT — YOUR HEALTH

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.

Hot water is a real cardiovascular load. Stand up slowly, hydrate, skip alcohol, and don't soak alone. Get out at the first sign of dizziness, nausea, or headache.

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 and soaks.