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 18.6 or later, and Apple Watch running watchOS 11.6 or later, which records your sessions and heart rate. Apple Watch Ultra adds automatic submersion detection and water-temperature sensing for cold plunges and soaks.
I really like this app because I no longer have to guess how long I need to sit in the sauna. I always knew that the time I want to be in the sauna varies based on my location and being in Texas vs Alaska, I can finally dial that in without having to guess all the time.
Hormetic 1.7 — a cleaner look, and less tapping.
• Favorites and routines: save a setup once and start it from your Watch with one tap and a 3-second countdown you can cancel. Build a routine on iPhone or Watch and move through it with Next.
• A new Watch start screen: Heat, Cold and Spa up front, with favorites and routines one swipe away.
• Adapt, redesigned: your week at a glance, with big tiles, trends and a dry-sauna visits ring. Its default of 4 comes from the Finnish KIHD study's "4–7 times a week" group, as a reference, not a recommendation.
• Compare two sessions of the same type side by side.
• Log filters for today, this week, session type and dates.
• Home Screen and Lock Screen widgets with your week's rings and bars, off until you turn them on.
• Apple Fitness now lists new sessions by what they were, such as Dry Sauna, Cold Plunge or Hot Tub, instead of "Other".
• An optional live view on iPhone of the session running on your Watch.
Every estimate is still labeled "Estimated", and your data still stays on your device.
Version 1.7.0
The developer, Avesta Forge LLC, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .
Data Not Collected
The developer does not collect any data from this app.
Privacy practices may vary, for example, based on the features you use or your age. Learn More
Accessibility
The developer has not yet indicated which accessibility features this app supports. Learn More
Information
Seller
Avesta Forge LLC
Size
10.5 MB
Category
Health & Fitness
Compatibility
Requires iOS 18.6 or later.
iPhone Requires iOS 18.6 or later.
Mac Requires macOS 15.6 or later and a Mac with Apple M1 chip or later.