While there is a low possibility of catching HIV through sex with another woman, it doesn’t mean you shouldn’t be careful.
It’s always wise to take precautions when you have any kind of sex, and you shouldn’t become complacent just because you are two women. For example, the highest risk times are when you have your period or if either of you have any cuts, either internally or around the entrance to the vagina.
HIV can be transmitted through blood, so if one of you has your period and the other suffers from gingivitis (bleeding gums) it is highly advisable to use a dental dam. A dental dam is a square piece of flexible plastic that can be placed over the entrance to the vagina. If you don’t have one, you can always cut up a condom to use instead.
If you are using toys, make sure they are washed before use and avoid sharing the same toy. If you do – use a condom.
The most important thing to remember is, that if either of you sleeps with men, make sure you use protection and tell each other about your status. The risks may be low, but that doesn’t mean there is absolutely no risk whatsoever. If you are unsure about something, it’s better to be safe and wait.