Heatstroke is when the body shuts down due to pressure from extreme temperatures. At this point, the body is unable to control its temperature. The body’s temperature spikes up and perspiration fails to cool it down. Heatstroke occurs after prolonged exposure to physical exertion in high temperatures. At this time, the body temperature reads at 104 degrees Fahrenheit or more. It is preceded by other types of heat injuries, one of which is heat exhaustion.
Heat exhaustion can be described as the early stage of heatstroke.  This is the period when the body starts to overheat but before it reaches 104 degrees Fahrenheit, causing heatstroke. Common symptoms include general muscle weakness, excessive sweating, nausea, vomiting, and fainting.
Heat exhaustion may be treated at home and symptoms often fade away after thirty minutes. Where symptoms continue for an hour or more, it may be a sign of an impending stroke. Heatstroke is the most serious form of heat injury and is described as a medical emergency. If left unattended, the patient may develop complications like damage to the brain, muscles, kidney, or heart. It can also lead to death. Heatstroke is a more serious condition than heat exhaustion. 
Here are some of the factors that can cause heat injuries: