Health is more than skin-deep -- as is its most pervasive adversary. Invisible and symptom-free, chronic inflammation is a factor in heart disease, some types of cancer, asthma, Alzheimer's, even aging itself. "Cooling the fires of hidden inflammation may be the most important thing you can do for your long-term health and well-being," says Dr. Mark Hyman, editor in chief of Alternative Therapies in Health and Medicine. Our four-step plan, covering food choices, weight management, exercise, and stress reduction, can help keep you healthy from your cells on up.

Whether you scrape your knee, twist your ankle, or succumb to strep throat, the body's reaction is the same: The immune system sends in an army of white blood cells to destroy bacteria and repair the tissue. This healing process, called the inflammatory response, is one of the body's most basic survival instincts. Under normal conditions, inflammation's hallmark signs -- redness, swelling, soreness, and warmth -- stay localized and disappear as the injury or infection heals. But sometimes the immune system does not shut off, instead releasing a stream of inflammation-promoting compounds that spread throughout the body, damaging cells and tissues. "Inflammation is a very effective mechanism for fighting off invaders," says Dr. Peter Libby, chief of cardiovascular medicine at Brigham and Women's Hospital in Boston. "But when the body is exposed to invaders for long periods of time, the defense mechanisms can be turned against us."

If left unchecked, low-level systemic inflammation can simmer for years, contributing to a range of seemingly unrelated ailments. Recent research shows that it can weaken cholesterol deposits in the coronary arteries, leading to heart disease; trigger bronchial tubes in the lungs to swell, causing asthma; or set the stage for abnormal cells to proliferate and become invasive cancers. "Inflammation is a key cause or factor in almost all chronic degenerative and lifestyle diseases," Hyman says.

What ignites the fire in the first place? Repeated or prolonged ailments, such as sinus or bladder infections, gingivitis, or stomach ulcers, can trigger chronic inflammation, as can food allergens, pesticides, even unremoved surgical sutures. In some cases, as with Crohn's disease (marked by inflammation in the small intestine), the cause is unknown.

Perhaps the most dangerous aspect of chronic inflammation is its stealthy nature; people often don't know they have it. Unless you have a painful inflammatory disease like lupus or rheumatoid arthritis, you might not have any symptoms at all. To detect silent inflammation, physicians measure blood levels of C-reactive protein (CRP), a substance found in the blood when systemic inflammation is present. When doctors find elevated CRP levels, they often do additional tests to determine what's triggering the inflammation and prescribe appropriate treatment. But "extraordinary science supports the very ordinary ways you can control inflammation," says Hyman. This diet, exercise, and stress-reduction plan can help.