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Get yourself checked out at a clinic, ask for an STD test, some places do them free, some not
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Before cunnilingus try and ask your partner if they have had an STD test, if they have and they are clean..... YOU'RE GOOD TO GO!!
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If you have cuts in your mouth then you could maybe try and avoid cunnilingus util they are all sealed up, having cuts gives a more direct root to the blood and therefore increases the probability of STD transmission
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If you get scared or they do have an STD use a "Dental-Dam" as unprinted suggested (and a condom for when it gets really hot :P )