There are a few factors that will affect how hot you get during work; The temperature, Wind speed, Humidity and radiant heat. If you have high blood pressure or take diuretics you may well be more sensitive to these heat factors.
The body will try to counter these effects by sweating and changing the blood flow. You may also begin to breathe harder. The body's first phase of defense is to pump the blood to the surface of the skin, This will allow your body to give off heat by increasing the skin temperature. Your body also sweats to cool off though this will only be effective if the humidity is low enough for the sweat to evaporate.
If your body gets too hot and over heats then a condition of heat stress will be present. Conditions of heat stress include heat stroke, heat cramps, heat exhaustion, heat rash and fainting.
Some of the signs and symptoms that you might have heat exhaustion for example will include sweating, Nausea, Weakness, Pale skin, sometimes clammy or flushed. In a situation like this you will need to rest up in a cool place and drink either water or an electrolyte drink, such as a sports drink. If the condition worsens or the person feints then call emergency services.
In situations where body temperatures increase to over 106oF it is likely that the persona has heat stroke. Call Emergency services straight away, then move the person into the shade. Cool the body down with water and fan.
It is important to know what to do in all situations of heat stress, so if you do work outside in the heat then be sure to research thoroughly all the do's and don'ts. You just may save someone's life one day.