WHO advises rinsing the hands well under clean, running water with soap for at least 20 seconds, irrespective of water being hot or cold.
Researchers from Vanderbilt Institute for Energy and Environment conducted a study. They found that close to 70 percent of people believed that using hot water is more effective than warm, room temperature, or cold water. Amanda R. Carrico, a research assistant professor, said that after reviewing the scientific literature, her team found 'no evidence that using hot water that a person could stand would have any benefit in killing bacteria.' Even water as cold as 40°F (4.4°C) appeared to reduce bacteria and hotter water if hands were scrubbed, rinsed, and dried properly. Using hot water to wash hands is therefore unnecessary, as well as wasteful, Carrico said.
Centers for Disease Control and Prevention (CDC) guides the usage of any temperature of water (cold or warm) to wash your hands are effective. Although for killing germs and viruses, the use of soap is necessary. Hands need to be scrubbed for at least 20 seconds.
According to the World Health Organization (WHO), hot water removes more protective fatty acids from the skin. Therefore, washing with hot water should be avoided, and also repeated exposure to hot water might increase the risk of dermatitis. Warmer water can irritate the skin and can affect its protective layer, which may cause it to be less resistant to bacteria.
Therefore, the CDC and WHO are do not specify water temperature, and hot water can result in some problems while washing hands.