Causes and Risk Factors
Both herpes and chickenpox/shingles are caused by previous exposure to HSV-1 or HSV-2 (for herpes), or to the varicella-zoster virus (for chickenpox/shingles).
One of the most important risk factors for shingles is age; about half of all patients are over 60 (Sampathkumar 2009; Fashner 2011). Patients aged 80 to 89 are 10 times as likely to develop shingles as children under age 10 (Albrecht 2012a). This age discrepancy is thought to be due to the gradual weakening of the immune system with age, a process called immunosenescence (Weaver 2009; Levin 2010).
Aside from increasing age, a suppressed immune system also increases risk of developing shingles (Weaver 2009; Fashner 2011; Mayo Clinic 2011; Albrecht 2012a). Patients who are immunocompromised have more manifestations of shingles, and these start earlier than in patients with healthy immune systems (Weaver 2009).
People who have diseases that weaken the immune system, especially HIV/AIDS, have an increased risk of developing shingles (Weaver 2009; Albrecht 2012a; Mayo Clinic 2011). The long-term use of immunosuppressive drugs, such as corticosteroids, increases the risk of developing shingles as well (Mayo Clinic 2011; Weaver 2009; Albrecht 2012a).
Some studies found that women are more likely than men to develop shingles, and African-American individuals are at lower risk than Caucasians (Tseng 2011; Albrecht 2012a).
For HSV-1 infection, there are no specific risk factors aside from increasing age, as the ubiquity of this virus means many will become infected; the University of Maryland Medical Center suggests that 62% of Americans are infected by the time they reach adolescence and that 85% of Americans in their 60s have contracted the virus (Ehrlic 2011a). Receiving oral sex increases the risk of developing genital herpes caused by HSV-1 (American Academy of Dermatology 2012; Ehrlic 2011a).
Risk factors for HSV-2 infection are primarily related to sexual activity, as this virus is typically spread via sexual contact. Engaging in sexual activity with a partner who has an active, symptomatic infection (ie, lesions on the genitals) is a very strong risk factor for transmission. Additional risk factors are female sex, having had many sexual partners, having had sexual encounters at an early age, and the presence of another sexually transmitted infection (Berger 2008; American Academy of Dermatology 2012; Ehrlic 2011a). Women have a higher risk of becoming infected with HSV-2 as a result of an unprotected sexual encounter than men (Ehrlic 2011a; Albrecht 2012b). People of African-American or Hispanic descent have a higher risk of HSV-2 than Caucasians (Berger 2008; CDC 2010).