There are no health risks if the hygiene is kept (as the previous poster stated, keep it clean before and after using it). I would also recommend to change different forms of stimulation during self-pleasuring in order to develop and keep a wider variety of sexually effective forms of stimulation. For some people it is possible to get "conditioned" to just one form of stimulation and then it can be difficult to get aroused or have orgasm in other ways during sexual activities, so in case of masturbation I would recommend to use different kinds of stimulation - hands, sex toys and so on - in order to keep the flexibility of sexual responses.
No. Keep it clean is all, you don't want to be introducing bacteria into your private parts. If anything, it should be a stress reliever, and better rather than worse for the cardiovascular system.