HIV (Human Immunodeficiency Virus) is a virus that attacks and breaks down the body's immune system - the "internal defense force" that fights off infections and disease. When the immune system becomes weak, we lose our protection against illness and can develop serious, often life-threatening, infections and cancers.
Getting sick is often a sign that your body is responding to invaders from the outside. For example, the pus around a splinter that gets infected is a sign of immunological effort — white blood cells building up to fight an infection. The same is true when your body’s immune system responds to HIV.
Anyone can get HIV—regardless of age, gender, gender identity, sexual orientation, income level, or ethnicity—but not everyone faces the same risk. Your risk comes from what you do, and who you do it with - that is, how likely it is that the person you have sex or share needles with is infected.