General Adaptation Syndrome (GAS): Hans Selye is credited with creating the first definition of stress as a non-specific response of the body to any demand made upon it. Selye's theory about the effects of stress he demonstrated to be applicable to any sort of stress.

The 3 stages of the GAS are:

• Alarm Reaction: Similar to fight or flight.
• Resistance: Struggle to overcome, hard work, limited rest/sleep.
• Exhaustion: Body systems crash, fatigue, errors, irritability, vulnerable to illness (colds, flu, acne).

Non-specific stress response: Selye's theory was that injury, overload and fear all produce the same body reaction. He believed that both eustress and distress both produced the same response in the body. Both situations, he said, resulted in some degree of wear and tear in the body which finally accumulated to produce aging.This theory was over-simplified as you will see below.