Many people think of inflammation in terms of external signs: swelling, bruising and so on. But in truth, uncontrolled inflammation plays a role in almost every major disease, including cancer, heart disease, diabetes, Alzheimer’s disease and even depression.

Inflammation is your body’s first line of defense against toxins, infections and injuries.

When your cells are in distress, they release chemicals to alert the immune system. The immune system sends its first responders — inflammatory cells — to trap the offending substance or heal the tissue. As this complex chain of events unfolds, blood vessels leak fluid into the site of the injury, causing the telltale swelling, redness and pain. These symptoms might be uncomfortable, but they are essential for the healing process.

Here’s the problem with inflammation: Over time, you can end up with too much of a good thing. With chronic inflammation, your body is on high alert all the time.

This prolonged state of emergency can cause lasting damage to your heart, brain and other organs. For example, when inflammatory cells hang around too long in blood vessels, they promote the buildup of dangerous plaque. The body sees this plaque as foreign and sends more of its first responders. As the plaque continues to build, the arteries can thicken, making a heart attack or stroke much more likely.

Similarly, inflammation in the brain may play a role in Alzheimer’s disease.  For many years the brain was thought to be off-limits to inflammation because of the blood-brain barrier — a sort of built-in security system — but scientists have proved that immune cells can and do infiltrate the brain during times of distress.