After invading the human body, HIV can integrate with human cells and is difficult to be removed from the body. It mainly affects the immune system, targeting the CD4+ T lymphocytes, which are the most important part of the immune system, and injuring the immune system, resulting in the loss of immune function. In the early stage of AIDS, i.e. the acute stage, the CD4+ T lymphocytes can drop rapidly, and then the CD4+ T lymphocytes can gradually return to normal within 1-3 weeks and enter the asymptomatic stage. Then CD4+ T lymphocytes can slowly continue to decline, after which CD4+ T lymphocytes decline rapidly again and enter the AIDS phase. After entering the AIDS stage, there can be persistent irregular fever of 38°C or higher for more than a month, and diarrhea for more than a month. Weight loss, up to 10% within six months, recurrent oral fungal infections, recurrent herpes simplex virus infections, recurrent bacterial pneumonia, Pneumocystis carinii pneumonia, including active tuberculosis, deep fungal infections, locoregional lesions of the central nervous system, young and middle-aged people can develop dementia, active cytomegalovirus infections, and toxoplasmosis, which can be life-threatening in severe cases. All of these conditions can be life-threatening in severe cases.