The human immunodeficiency virus (HIV) attacks the body’s immune system. A healthy immune system provides a natural defence against disease and infection. If the immune system is damaged by HIV, it increases the risk of developing a serious infection or disease, such as cancer.
HIV infects particular cells, called CD4 cells, that are found in the blood. CD4 cells are responsible for fighting infection. After they become infected, the CD4 cells are destroyed by HIV. Although the body will attempt to produce more CD4 cells, their numbers will eventually decline and the immune system will stop working.
For full details of HIV click here to be taken to the NHS Choices website. If you are worried you may be at risk of having an STI or have any symptoms (as mentioned on the NHS Choices link to HIV), you should visit your local sexual health or GUM clinic to have them checked out.
(Link checked as correct on 18/10/2013 by SA next update due 18/4/2014)