The risk of sharing sex toys (e.g. dildos, butt plugs and other objects meant to be inserted into the rectum and/or vagina) varies according to whether they are covered with condoms, and whether they are properly cleaned (i.e., disinfected) between use with different partners. Sex toys come into direct contact with rectal and/or vaginal mucosal membranes, which can both transmit HIV and are susceptible to infection. Shared an uncleaned dildo or other toy can transfer infectious fluids from an HIV-positive person to an uninfected person, and poses a high transmission risk.
If sex toys are used with new, clean condoms for each partner, or are properly cleaned (i.e., disinfected) before use by the uninfected partner, they pose a negligible risk of transmission. Note that using the same condom with both partners is effectively the same as not using one at all.
There is zero HIV transmission risk attached to using sex toys if they are not shared. However, sex toys are often used before or after other sexual activities. As with fingering, fisting and other forms of play, any tissue damage or inflammation that results from sex toy use can affect the risk of infection during other activities.