Even in winter, a water temperature of 110°F is still excessively high and unsafe for a spa hot tub. The professionally recommended safety limit remains 104°F (40°C), with the ideal range typically falling between 102°F and 104°F (39°C–40°C).

Studies show that: • Sitting still in 40°C hot water for 30 minutes can burn an additional 25–40 calories; • If the body's thermoregulation response is stronger (e.g., more sweating), it can reach 50–60 calories. In other words: A 30-minute hot tub bath can burn approximately 60–100 calories.

Many people believe that weight loss after a spa hot tub bath is due to "burning fat." In reality, the temporary weight loss is due to the body losing water, not fat. Therefore, while a spa hot tub can slightly accelerate calorie burning, it cannot replace exercise.

If you experience the following symptoms after using a hot tub, you should suspect bacteria in the water: • Skin rash, itching, burning sensation; • Folliculitis or pimple-like red spots; • Localized skin infection or pustules. These are often signs of a hot tub rash caused by bacterial contamination.

For people with heart disease, using a spa hot tub carries potential risks. • Patients with coronary heart disease; • Those with a history of arrhythmia or heart failure; • Those who have had a myocardial infarction; • People with pacemakers (must have their device's safety range confirmed by a doctor).

In unclean spa hot tubs, it often causes a skin condition known as "Hot Tub Folliculitis." This infection manifests as folliculitis, rashes, itching, and even pustules, usually appearing within 24 to 48 hours of exposure.