Thank you for your question. This painless swelling appears to be a a fluid filled blister on your glans penis. We are not certain if this was caused by a sexually transmitted infection. Painless smooth blisters such as the one you have cold be caused by syhilis. It is important that you have this blister examined by your doctor. Try not avoid sexual contact until after you have this examined and have the appropriate testing performed. Syphilis is caused by a bacteria called treponema pallidum. Early infections can start off as developing painless blisters in the genital region to infection of the central nervous system. It is important that you promptly see your doctor to have this examined.
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