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HIV (human immunodeficiency virus) is a virus that attacks the immune system and weakens your ability to fight infections and disease. AIDS (acquired immune deficiency syndrome) is the name used to describe a number of potentially life-threatening infections and illnesses that happen when your immune system has been severely damaged by the HIV virus. With early diagnosis and effective treatment, most people with HIV will not go on to develop AIDS.

In the UK, most cases of HIV are caused by having sex with a person who has HIV without using a condom. A person with HIV can pass the virus on to others even if they don't have any symptoms. People with HIV can pass the virus on more easily in the weeks following infection. HIV treatment significantly reduces the risk of someone with HIV passing it on.

HIV is found in the body fluids of an infected person, which includes semen, vaginal & anal fluids, blood, and breast milk.  It cannot be transmitted through sweat or urine.