“The stress at work is sending my blood pressure through the roof,” a patient told me. His instinct was good, because experts who study stress are increasingly seeing how it connects to illness. Stress affects your heart, weight, and skin. It’s also linked with physical training, an increased risk for developing depression, the common cold, and influenza, as well as associated with increased symptoms among those with chronic illnesses,” says Dr. Sheldon Cohen, a professor of psychology at Carnegie Mellon University in Pittsburgh.

Confronted by sudden danger, the human body instantly pumps the bloodstream full of adrenaline. This hormone, along with cortisol raises your:

• blood pressure
• heart rate
• blood sugar

temporarily giving you additional strength, speed, and stamina. In emergency situations, stress can save your life.

But ongoing stress—the kind you might face when you’re experiencing marital, financial, or work-related problems or are caring for a sick relative—influences your ability to function and may lower your immunity. Even your genes can be affected, says Dr. Elissa Epel, a health psychologist at UC, San Francisco, because stress changes “the protein output of our DNA.” That’s like saying it affects the core of what we are made of.

Here’s what else we know about stress and sickness.

Heart

“There is overwhelming evidence that stress creates an environment where heart attacks and even sudden death become more likely,” says Dr. Joel Dimsdale of UC, San Diego, in the Journal of the American College of Cardiology. Job stress has been found to increase cardiovascular risk by up to 50%. In addition, stress lowers estrogen production, which reduces protections against heart disease in women, explains Dr. Stephen Manuck, a professor of psychology at the University of Pittsburgh.

Headaches

Stress appears to change the balance of chemicals in the brain in a way that may contribute to the narrowing of blood vessels—one theory for why we get migraines. Stress also is a factor in tension headaches. And physical reactions to stress—such as tensing the neck and shoulders, grinding teeth, or clenching the jaw—may make headaches worse.