Harvard Mental Health Letter

Infection, inflammation, and mental illness

The body's immune response to infectious agents may imperil the brain.

For more than a century, researchers have explored whether infectious agents might trigger some types of mental illness, particularly schizophrenia. For the most part, however, these theories rested on studies that proved only an association between certain infections and mental disorders, not cause and effect.

But since 2000, researchers have produced a growing body of observational and biological evidence suggesting that the body's defensive immune response, rather than the infection itself, may be what damages the brain. Further, chronic stress may activate a harmful immune response, even in the absence of infection. Although the research remains preliminary, the findings could suggest a new approach to treatment.

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