Unprotected sex: If a person engages in sexual intercourse with an infected person without using a condom, he/she can get infected. The sexual act can be both vaginal and anal.

Sharing of needles: If a person shares the needle or syringe used by/on an infected person, either for injecting drugs or drawing blood or for any other purpose involving piercing, he/she can get infected. Instruments used for piercing and tattooing also carry a small risk of infection.

Unsafe blood: A person can get the infection, if he/she is given transfusion of infected blood.

Improperly sterilized hospital tools: If surgical devices like syringes and scalpels, or even certain instruments, used on an infected person, are used on another person without proper sterilization, they can transmit the infection.

Mother to Child: An HIV positive mother can transmit the virus to child during pregnancy or birth. Breast milk can also act as a transmission-medium.Theoretically oral sex without condom (on men) or barriers like dental dam, vaginal dams or plastic wrap (on women) can also transmit the infection.