Phones and Electronics: Why They Stay Outside

How hot does a sauna get?

A traditional sauna typically runs between 150°F and 195°F (65°C to 90°C), according to the Cleveland Clinic, with humidity usually below 20%. Infrared saunas operate at lower air temperatures, usually between 110°F and 135°F (43°C to 57°C). The heat is not just ambient: it penetrates into anything left inside the room, including your phone.

Finnleo, a sauna manufacturer, notes that many people enjoy their traditional sauna between 150°F and 175°F, and infrared models between 120°F and 130°F. Those temperatures are far above the range most consumer electronics are designed for. Even a single session can stress internal components.

If you prefer a classic high-heat experience and will keep your phone far away, check out our best traditional sauna gear guide. For a lower-temperature option that is easier on electronics left nearby, see our best infrared sauna gear guide.

What heat does to batteries

Modern phones use lithium-ion batteries, which rely on controlled chemical reactions. High temperatures accelerate those reactions, leading to reduced capacity, swelling, and in extreme cases, permanent damage. A battery left in a hot sauna can lose its ability to hold a charge and may even bulge, putting pressure on the phone's case and internal connectors.

The heat also affects the battery's safety circuitry. If the battery gets too hot, the risk of thermal runaway increases. Thermal runaway is a self-sustaining reaction that can generate more heat and, in the worst case, start a fire. This is why sauna guidelines universally advise keeping electronics out.

Signs that a battery has been overheated include a swollen case, a cracked screen lifting away from the frame, rapid discharge even after charging, and the phone feeling unusually warm when idle. If you notice any of these, stop using the device and have it checked by a professional.

To avoid these issues, always leave your phone in a dry, cool place outside the sauna. For a comprehensive list of items that should never cross the sauna door, see our article on what not to bring in.

Screens and other components

Screens are also vulnerable. The adhesive that bonds the display layers can soften at high temperatures, causing delamination and air bubbles. LCD and OLED panels can also suffer permanent color shifts or dark spots if exposed to intense heat for extended periods.

Plastic components, including buttons, camera lenses, and charging ports, can warp or discolor. The internal circuit board may experience solder joint stress as components expand and contract at different rates. While one short session may do little, repeated exposure will steadily degrade the device beyond repair.

High humidity in steam rooms and wet saunas adds another threat. Moisture can seep into unsealed ports and corrode contacts. Even if your phone is water-resistant, the combination of heat and steam can break down seals over time. For more on humidity levels, see our article on sauna humidity and temperature terms.

The fire risk

The most serious concern is fire. A lithium-ion battery that fails can ignite, and a sauna is full of combustible materials like wood benches, towels, and the sauna structure itself. A small electronics fire can quickly grow in an enclosed wooden room.

Sauna safety guidelines emphasize that heat sources should never be blocked or placed near flammables. A phone left on a bench or tucked into a towel can trap heat and accelerate battery stress. It's not just about protecting the device; it's about protecting everyone in the room.

For a thorough overview of precautions, read our sauna fire safety basics article. You should also be aware of the what not to bring in list, which covers items that pose similar risks.

Keeping your phone safe

The simplest rule is to leave your phone outside the sauna room in a dry, cool area. A pocket in a jacket hung in the changing area works well, but avoid leaving it in direct sunlight or near any heat source. If you use your phone for music or a timer, place it far from the heater and never on a bench or towel.

If you need to stay connected for emergencies, consider a phone lockbox or a sealed bag placed outside the sauna, but these do not protect against ambient heat if they are inside the room. The best approach is to fully disconnect and enjoy the heat, which also enhances the mental benefits of your session.

For those who want to combine sauna use with electronics, a portable sauna with a separate control unit often allows you to keep your phone outside the heat zone. Explore our best portable saunas guide for options that suit this need.

What about electromagnetic fields?

Some people wonder if phone radiation is a concern in a sauna. The National Cancer Institute and the National Institute of Environmental Health Sciences explain that cell phones emit non-ionizing radiation, which is not known to damage DNA or cells. The scientific evidence has not conclusively linked cell phone use with any adverse human health problems, according to the National Institute of Environmental Health Sciences.

Thus, the main reason to leave your phone outside is heat, not electromagnetic fields. If you still want to keep a phone nearby for music or timers, place it outside the sauna room, far from the heater, and avoid leaving it in a towel or direct warmth. To learn more about EMF in sauna contexts, see our article on what EMF means in saunas.

What to pick for your sauna setup

Questions

Can I bring my phone into a sauna if it's in a waterproof case?

A waterproof case protects against moisture, not heat. The internal temperature of the phone will still rise, and the battery is still exposed to the same thermal stress. Keep the phone outside. For a list of items to leave behind, see our what not to bring in guide.

How long can an electronic device survive inside a sauna?

There is no safe duration. Even a few minutes at typical sauna temperatures can cause permanent damage to battery health and display adhesives. The longer the exposure, the greater the risk of failure. To learn about related risks, review our sauna fire safety basics.

Is it safer to use a phone in an infrared sauna at lower temperatures?

Infrared saunas operate at lower air temperatures, but the heat still exceeds what consumer electronics are designed for. The lower temperature reduces but does not eliminate the risk. Leaving your phone outside is still the recommended practice. If you are considering an infrared model, see our best infrared sauna gear guide.

What should I do if my phone gets too hot?

Turn it off, move it to a cool, dry area, and let it return to room temperature gradually. Do not place it in a fridge or freezer. If the battery swells or the phone emits smoke, move away and call emergency services. Understanding the risks is the first step, and our sauna fire safety basics article explains more.