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For more information, see our Fact Sheet that covers the basics on defining, contracting and treating HIV and AIDS.

What are HIV and AIDS?

HIV (Human Immunodeficiency Virus) is a virus that weakens the body's defense (immune) system until it can no longer fight off illnesses such as pneumonia, tuberculosis, cancerous tumors and others. HIV kills your CD4 cells (T cells), which direct your body's immune system to defend against infection.

You are considered to have AIDS (Acquired Immunodeficiency Syndrome) when your immune system is seriously damaged by HIV. In the U.S., an HIV-infected person receives a diagnosis of AIDS when his/her CD4 count is less than 200 or if diagnosed with a specific illness. (An average CD4 cell count in a healthy person is 1,150.)

How Might I Become Infected with HIV?

HIV is transmitted from an HIV-positive person through infected body fluids such as semen, pre-ejaculate fluid, blood, vaginal secretions or breast milk. HIV can also be transmitted through needles contaminated with HIV-infected blood, including needles used for injecting drugs, tattooing or body piercing. HIV is most often transmitted sexually.

How Does HIV Work Inside the Body?

Watch "What HIV Does Inside the Body" for a short, informative explanation of how HIV attacks and affects your health.

How Can I Protect Myself from HIV?

You are safest if you do not have sexual intercourse, oral sex or share needles or injection equipment.with an HIV-positive person. You are also safe if you are in a relationship in which both you and your partner are monogamous and have been free of HIV for six months. Whenever you are unsure about the risk of infection, always use a latex barrier when having sex of any kind - vaginal, oral or anal.

Why Should I Be Tested?

Knowing you are HIV-positive will allow you to seek early treatment that could help you stay healthy longer. Whether you are HIV-negative or HIV-positive, you can learn how to prevent future infection with HIV or other STDs through the counseling at many testing centers.

What Does "Undetectable" Mean?

Undetectable means that there is so little HIV in your blood that it can't be measured by a test. Watch "The Goal of Undetectable" to see how you can protect your health and the people you care about.

HIV Hotline

You can reach the HIV Hotline at 1-800-228-0469.

Page last updated: December 13, 2023