Stress affects everyone and needs to be effectively managed to avoid negative consequences. Stress was first conceptualized in the 19th century and is defined as any demand placed on the body. The fight or flight response is the body's instinctual reaction to stress. Stress has physical, psychological, and behavioral effects and builds up over time if not managed properly. While some stress can be positive, too much stress weakens the immune system and increases health risks. Managing stress requires techniques like breathing, exercise, meditation, and optimism.