HIV/AIDS denialism is the refusal to acknowledge that human immunodeficiency virus (HIV) causes acquired immune deficiency syndrome (AIDS), despite the conclusive evidence. Some of its proponents reject the existence of HIV, while others accept that HIV exists but argue that it is a harmless passenger virus and not the cause of AIDS. Insofar as they acknowledge AIDS as a real disease, they attribute it to some combination of sexual behavior, recreational drugs, malnutrition, poor sanitation, haemophilia, or the effects of the medications used to treat HIV infection (antiretrovirals).