How Shingles is Contracted
Shingles is not "contracted" from another person—it develops from reactivation of the varicella-zoster virus (VZV) that has been dormant in your nerve cells since you had chickenpox, triggered primarily by declining cell-mediated immunity. 1, 2
The Reactivation Mechanism
After you recover from chickenpox (which you do contract from others), the varicella-zoster virus doesn't leave your body—it establishes permanent latency in your sensory nerve ganglia (dorsal root ganglia). 1 The virus remains suppressed there for decades by your VZV-specific cellular immunity. 2 When this specific immune surveillance weakens sufficiently, the dormant virus reactivates, travels along the sensory nerve pathway, and erupts as the characteristic painful, unilateral dermatomal rash of shingles. 2, 3
Why Reactivation Occurs After Age 50
- Age-related immunosenescence is the primary driver: Your VZV-specific cell-mediated immunity naturally declines with aging, which is why incidence rises sharply after age 50. 1, 2
- Approximately 20-30% of people will develop shingles over their lifetime, with rates of 7-10 cases per 1,000 person-years after age 50. 1, 3
- Nearly all adults over 50 harbor latent VZV—95-99% of adults in the U.S. have been infected with VZV and carry the virus capable of reactivation. 2
Additional Risk Factors for Reactivation
Beyond age, specific conditions accelerate the decline in VZV-specific immunity: 2, 3
- Immunosuppressive conditions: HIV/AIDS (15-fold higher risk), diabetes mellitus, rheumatoid arthritis, systemic lupus erythematosus, inflammatory bowel disease (risk ratios 1.23-2.08) 2, 3
- Immunosuppressive medications: High-dose corticosteroids (≥7.5 mg/day prednisolone), JAK inhibitors (3-4 times higher risk), biologic DMARDs, chemotherapy 3
- Other triggers: Psychological stress, ultraviolet light exposure, fever, recent COVID-19 infection 2, 3
- Early childhood chickenpox: Children who had chickenpox during the first year of life have increased risk of childhood shingles 1
Important Distinction: Transmission FROM Shingles
While you cannot "catch" shingles from someone else, a person with active shingles can transmit VZV to susceptible individuals (those who never had chickenpox), causing chickenpox in them—not shingles. 1 The transmission risk from shingles lesions is approximately 20% of the risk from active chickenpox. 1 The infected person remains contagious from 1-2 days before rash onset until all lesions are crusted. 1, 2
Clinical Pitfall to Avoid
Do not confuse the mechanism of shingles development with chickenpox transmission. Chickenpox spreads person-to-person via direct contact, airborne droplets, or respiratory secretions with 80-90% attack rates in susceptible household contacts. 1 Shingles, however, is an endogenous reactivation—you're essentially being "infected" by your own latent virus when your immune system can no longer suppress it. 2, 3
Vaccine Considerations
Even individuals who received varicella vaccine (rather than natural chickenpox) harbor latent vaccine-strain VZV in their ganglia and remain at risk for shingles, though this risk appears lower than after wild-type infection. 1, 2 Vaccination with recombinant zoster vaccine (RZV) boosts VZV-specific T-cell immunity and is the most effective prevention strategy, reducing shingles incidence by 92% over 3.2 years. 4