Water can cause full-thickness third-degree burns after five seconds of exposure at 140 degrees Fahrenheit, according to the Burn Foundation. One second of exposure to water at 156 degrees Fahrenheit or two seconds of exposure to water at 149 degrees causes third-degree burns.
Because a child’s skin is more susceptible to burns, bath water should not be hotter than 100 degrees Fahrenheit, notes the Burn Foundation. There are more than 500,000 scald burns in the United States each year, and 17 percent of all childhood hospitalizations for scald injuries are due to hot tap water. In children under age 4, scalds are the No. 1 cause of burn injuries.