If untreated, people living with HIV progress from having no symptoms to developing illness and late-stage infection, ending with AIDS. 

Left untreated, HIV infection goes through the following stages:

1. Seroconversion illness

Some people experience a short illness soon after they contract HIV (3-6 weeks). This is known as seroconversion illness or primary or acute HIV infection.

In some people, seroconversion illness is so mild that it passes without being noticed. Some people mistake it for the flu, but for others it’s more severe and they may need to see a doctor.

Seroconversion is the period when someone with HIV is at their most infectious.

2. The asymptomatic stage of HIV

Once seroconversion is over, most people feel fine and don’t experience any symptoms. This is often called the asymptomatic stage and it can last for several years.

Though you might feel well at this stage, the virus is active, infecting new cells, making copies of itself and damaging your immune system’s ability to fight illness.

3. Symptomatic HIV 

The longer you live with HIV without treatment, the greater your risk of developing infections that your weakened immune system can’t fight: certain cancers, as well as the direct effects of HIV.

Getting ill in one of these ways means that you now have symptomatic HIV.

4. Late-stage HIV

If HIV has a chance to cause a lot of damage to your immune system, you may become ill from certain serious opportunistic infections and cancers. These illnesses are also known as AIDS-defining.

AIDS-defining illnesses:

• cancer
• tuberculosis (TB)
• pneumonia

Most people living with HIV never experience late-stage HIV, though it depends on a range of factors, including how soon you start treatment, how well you respond to it and what lifestyle you lead.