When the summer heat makes you feel tired, it's not just a hallucination: there are real scientific reasons for the lethargy.

　　Temperatures have soared this summer, setting records of the hottest season in history. The high temperatures are not only taking a toll on people's physical fitness, but also making people suffer from summer lethargy, a seasonal feeling of fatigue that includes multiple symptoms such as loss of appetite, fatigue, headaches and dizziness.

　　According to experts, summer fatigue is mainly caused by the long exposure to sunlight that many people experience during the summer.？Due to the longer duration of sunlight, melatonin production is affected, which influences our sleep. Also, the higher temperatures make it harder for the body to maintain a balanced internal temperature. This extra effort can make you feel more tired.

　　In order to maintain a stable body temperature, vasodilatation is required. Vasodilation is the process by which your blood expands, allowing more blood to flow near the surface of your skin, which releases heat.

　　The process not only allows you to cool down, but can also make you appear "flushed" and feeling tired.

　　Sweating is another process that can keep our bodies cool. Sweating allows the skin to cool down as the sweat evaporates.

　　On the inside, however, sweating causes both a person's heart rate and metabolic rate to increase, which can consume massive amounts of energy. Excessive sweating can make you extremely tired and sleepy.

　　Another reason people feel tired on hot days is sleep deprivation. A 2022 study found that for every degree of warming, people get a little less sleep. The study's lead author, Kelton Miner, a postdoctoral research scientist at Columbia University's Data Science Institute, said that when nighttime outdoor temperatures exceeded 10°C, people lost an average of 37 seconds of sleep per night for every 1°C increase.

　　Whether you are at the pool, in the yard, or just relaxing in the shade, hot temperatures will eventually make you feel tired. The best way to stop or even reverse this is to stay hydrated, since hydration replaces the fluid lost through sweating.