The immune system protects the body against infection and disease. Some conditions and medications can weaken the immune system and set off reactivation of the virus that causes shingles. A weak immune system cannot effectively fight developing infections and illnesses.

Factors that may weaken the immune system, reactivate the chickenpox virus, and cause shingles include:

• Being age 50 or older.
• Recent surgery.
• Drugs or certain medications that suppress the immune system (immunosuppressive drugs).
• Radiation therapy.
• Serious illness or disease, such as cancer or AIDS.
• Poor nutrition.
• Stress.
• Chronic diseases that suppress the immune system, such as diabetes, lupus, or HIV.
• Injury.
• Organ transplant.