The definition of safe sex, for most people that means using a condoms during sex, whilst that is important, one tends to forget that there are other forms of sex which also requires protect,
A lot of people might not know that, unprotected oral sex can also transmit STI, there are many STI that can be easily transferrable via Oral Sex, if you have multiple sexual partners and you often engaged in unprotected oral sex, you could be at risk at STI.
My Advice is that if that is the case, use protection, there are dental dams out that that are specifically designed for oral sex, both for females and males