Your body does a poor job of distinguishing between life-threatening events—the house is on fire!—and minor-league stressful situations. No matter what the trigger is, your heart beats faster than normal, you breathe more quickly, your blood pressure rises, and your muscles prepare to spring into action. Anger or anxiety triggered by less momentous sources of stress, such as financial worries, traffic jams, or even worry about problems that haven't actually occurred, doesn't find a quick physical release. Instead, it tends to build up as the day wears on. Physical and psychological symptoms of stress—a clenched jaw, shakiness, anxious feelings—compound this, creating a negative, self-perpetuating cycle that may prompt health problems over time.
High blood pressure, a major risk factor for heart disease and stroke, is a prime example. Another is suppression of the immune system, which slows healing and makes you more susceptible to colds. Stress may contribute to, or exacerbate, many health problems, including allergic skin reactions, anxiety and depression, headaches, heartburn, irritable bowel syndrome, and pain springing from various conditions.