Cold sore on lip

Out of sight

Some infections are with us for life

Some microorganisms can lie latent in our cells for months or years. Although they may not multiply and don’t cause disease during this time, they remain undefeated by the immune system.

A common example is herpes simplex virus 1 (HSV-1), which causes cold sores. It persists in nerve cells in the peripheral nervous system (outside of the brain and spinal cord) and can be reactivated by factors like stress, illness or sunlight to cause new cold sores.

Another herpes-type virus is cytomegalovirus, which causes severe developmental abnormalities if contracted by an unborn baby. In children and adults, cytomegalovirus might cause only one bout of flulike disease, but it takes up lifelong residence in the body just like HSV-1. Cytomegalovirus can recur and cause more-serious problems in people with weakened immune systems, like those undergoing chemotherapy.

Lead image:

Leonardo da Silva/Flickr CC BY NC


About this resource

This resource was first published in ‘Immune System’ in January 2015.

Immunology, Health, infection and disease
Immune System
Education levels:
16–19, Continuing professional development