Dildos and buttplugs can be involved in the transmission of HIV, hepatitis A, B and C as well as other STIs, and a variety of gut infections if you share them.
Anal mucus or blood from a person on sex toys could lead to infections if the same toys are then used on someone else. Using toys may cause damage to the lining of the rectum. This damage can be microscopic, removing just the surface layer of the rectum’s lining so it won’t necessarily be severe or cause bleeding. If sex toy play is followed by unprotected anal, this damage means there is a greater chance of HIV & STI transmission.
The easiest way to avoid this is not to share sex toys.
You can also use a condom to cover the dildo, and change it between partners if using it on more than one person. Washing sex toys thoroughly after use, using warm soapy water or a sterilising fluid designed for baby bottles, should prevent any infection remaining on the toy.
Other toys like Fleshlites and sheaths should be cleaned between users to avoid passing on HIV or other STIs. If a guy with HIV or an STI cums inside a Fleshlite and another guy uses it afterwards, he could catch HIV or an STI through his foreskin, the head of his penis or his urethra.
The same is true of wanking sheaths. As with dildos, you should wash all toys thoroughly after use, using warm soapy water or a sterilising fluid designed for baby bottles. This should prevent any infection remaining on the toy.