Can you wear an Apple Watch in a sauna?

Apple answers this on its own support page, and the answer is narrower than most people expect. Only Apple Watch Ultra is advised for a sauna at all, and only up to 55 °C. Every other model, and every model in a steam room, is on the list of things to avoid.

What Apple says

Apple’s page on Apple Watch water resistance, published 14 September 2026, lists three heat-related things among those to avoid: wearing any model other than Apple Watch Ultra or later in a sauna, wearing Ultra or later in a sauna above 55 °C (130 °F), and wearing any Apple Watch in a steam room.

The page sits under water resistance, and it does not say what goes wrong above the limit. It does not need to. The guidance is specific, it is current, and it comes from the company that makes the watch.

Three things follow from it, and they are worth keeping separate:

How hot a sauna actually is

A traditional Finnish sauna runs somewhere between 70 and 100 °C. The long-running Finnish cohort studies that most sauna health claims trace back to followed men using saunas at about 79 °C. Infrared cabins are a different design and usually run much cooler.

So the 55 °C limit rules out a typical sauna for every Apple Watch, the Ultra included. What it leaves is an infrared cabin, or a sauna deliberately run cool. If you do not know your sauna’s temperature, a cheap thermometer at head height on your usual bench will tell you, and it is worth knowing for its own sake: the temperature near the ceiling can be far above the reading on a dial mounted lower down.

What this means for heart rate in the sauna

Heart rate needs the watch on your wrist. If the watch should not be in the room, there is no heart rate for that round.

That is a real loss, because heart rate in the heat is interesting. In one Finnish study at 80 °C, heart rate rose about 60% in dry air and about 130% once the air was made humid. But the honest position is that a wrist-worn Apple Watch is not the instrument for measuring it in a hot sauna, and nothing on this site or in the app should suggest otherwise.

Two measures in Contrast read heart rate during heat rounds: heart work in the heat, and heat strain. Both work fully for hot baths, which run 38 to 42 °C and are not on Apple’s list. For saunas they work only with an Ultra in a sauna kept below 55 °C.

Timing a sauna round with the watch outside

A sauna round in Contrast opens on a tap, and its length is the time from that tap to your next one. It does not depend on heart rate arriving, and nothing in the app interrupts a round because the watch has come off your wrist.

So the practical routine is short. Before you go in, tap Switch and pick sauna. Take the watch off and leave it outside. When you come out, put it back on and switch to whatever is next, whether that is a plunge, rest or the end of the session. The sauna round is recorded with the right duration and no heart rate, and it counts towards your weekly heat minutes and the sauna habit comparison the same as any other.

If you would rather not handle the watch at all, log the session on your iPhone afterwards: when it started, each round, and the sauna’s temperature if you know it.

What the watch can do in the heat

A hot bath is the case the guidance does not cover. Apple’s page lists saunas and steam rooms and does not list hot baths or hot tubs, and a bath is far cooler than a sauna. Contrast makes no claim beyond what Apple’s page says. On an Apple Watch Ultra or Series 10 and later, getting into a hot bath starts the round on its own, and the water temperature, read every round, splits the time into temperature bands.

Safety, separately from the watch

Sauna is well tolerated by most healthy adults. Unstable angina, a recent heart attack and severe aortic stenosis are reasons to avoid it, and alcohol raises the risk of low blood pressure and arrhythmia in the heat. Check with a doctor first if you have a heart condition, high or low blood pressure, or are pregnant.