The cells in your body are always producing heat from the energy stored in the food we eat. This heat is needed to keep your vital organs at 37 degrees Celsius (98.6 degrees Fahrenheit) at all times. Depending on the temperature of the environment, your body can regulate the amount of heat produced and, to an extent, how much it loses to the environment.
However, if the environment temperature is around 30 degrees Celsius (86 degrees Fahrenheit), your body loses this internal heat much slower, as there is less of a temperature difference between your body and its surroundings. Yet your body still needs to produce heat to keep you warm on the inside, so you feel hot.
Answered by Rik Sargent