HIV and AIDS: Prevention and risks

Preventing HIV

There are several treatments that prevent the transmission of the human immunodeficiency virus (HIV).

While treatment can prevent HIV transmission, you should still protect yourself against other sexually transmitted infections (STIs), such as:

Other methods of protection, such as condoms, can help prevent STIs.

Treatment as prevention

HIV treatment improves the health of people living with HIV and is a highly effective strategy to prevent HIV transmission.

HIV treatment can reduce the amount of virus (viral load) in the blood and other bodily fluids (like semen, and vaginal and rectal fluids) to very low levels. When the amount of virus is less than 200 copies of virus per millilitre of blood, it's called viral suppression.

People living with HIV who are on treatment, engaged in care and maintain a suppressed viral load have no risk of transmitting HIV to their sexual partners.

This is also known as "Undetectable = Untransmittable" (U = U). It references the fact that many standard HIV tests can't detect a supressed viral load.

Undetectable = Untransittable

Pre-exposure prophylaxis (medication)

People who are HIV-negative can take medication called pre-exposure prophylaxis (PrEP) to help prevent them from getting HIV. Taking PrEP also involves:

  • seeing a doctor or nurse every 3 months for HIV testing
  • screening for other STIs
    • medication should be taken in combination with safer sex practices to lower the transmission risk
  • monitoring for possible side effects
  • ongoing support

When PrEP is used consistently and correctly, it's rare for HIV to be transmitted through sex.

PrEP can be less effective when pills are missed because drug levels in your body may be too low to prevent HIV infection.

This medication does not prevent pregnancy.

If you want to take PrEP, talk to your health care provider. Any doctor can prescribe PrEP and some nurses are also licensed to prescribe it.

Post-exposure prophylaxis (medication)

Medication called post-exposure prophylaxis (PEP) reduces the risk of contracting HIV. It involves taking HIV medications as soon as possible after a potential exposure to HIV. PEP means taking daily pills for 4 weeks.

PEP is very effective but won't prevent 100% of HIV infections. It must be started as soon as possible after an exposure to HIV, ideally within 72 hours.

If you think you may have been exposed to HIV, immediately contact your health care provider, a hospital emergency room or sexual health clinic to see if they offer PEP.


Because the most common way to transmit HIV is through sexual activity, using condoms can reduce your risk of contracting or transmitting the virus.

You're at risk if you:

  • have condomless vaginal or anal sex with someone who is HIV-positive and isn't on treatment and virally suppressed
    • virally suppressed means the amount of virus in the person's system is too low to be measured on a standard blood test
  • perform oral sex without a condom
    • this is considered low risk unless you have open sores or cuts in your mouth

Reducing your risks

Injecting drugs

If you inject drugs, you can reduce the risk of contracting or transmitting HIV by following safe injection practices.

Avoid sharing drug injection equipment, such as:

Use new equipment every time you inject.

You may get help by signing up for a treatment program on substance use, such as:

Such programs can help you reduce your:

Pregnancy and childbirth

If you're pregnant or plan to become pregnant, you and your partner should be tested for sexually transmitted and blood-borne infections (STBBIs), including HIV. Even if you have HIV, you have effectively no risk of transmitting the virus to your baby if you:

Tattooing, body piercings, acupuncture and other procedures

If you're getting a tattoo, body piercing, electrolysis or acupuncture, you can avoid contracting or transmitting HIV by asking if:

Universal precautions (CATIE) (PDF)

Medical tourism

If you're travelling to another country for medical care, ask if the:

Workplace exposure

If your job exposes you to blood or other bodily fluids, you may be at risk for HIV infection.

You can reduce your risk by following routine practices for controlling infection in your workplace.

Routine practices for hazard prevention and control (Canadian Centre for Occupational health and Safety)

Related links

Page details

Date modified: