Thank you for your inquiry. From what we gather from the question, you were asking about the possibility of HIV transmission after receiving oral sex and performing oral sex without a barrier.
From the information provided, the former scenario is considered to be Negligible Risk (there is no evidence or no documented cases of transmission, however, there is a theoretical possibility of transmission under certain extenuating circumstances), while the latter scenario is considered to be Low Risk (evidence of transmission occurs through these activities when certain conditions are met).
From the HIV Transmission Equation (see image below), HIV transmission requires HIV particles in a bodily fluid (e.g. vaginal fluids) to have direct access to the bloodstream through a High, Low, or Negligible Risk activity. This could potentially occur during oral sex if HIV-containing bodily fluids gain direct access to your bloodstream such as through sores in the mouth, vagina, penis; bleeding gums; and/or oral contact with menstrual blood (1).
The easiest way to lower the risk of transmitting HIV through performing or receiving oral sex is to use a barrier such as a condom or dental dam (1). One can reduce the risk even further if an HIV-negative partner is taking medicine to prevent HIV (pre-exposure prophylaxis aka PrEP) or an HIV-positive partner is taking medicine to treat HIV (antiretroviral therapy aka ART) and is virally suppressed (1).
Recommendation: Refer to a health care provider for HIV testing.Take care,
AIDS Vancouver Online/Helpline, Shirley
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(1) Oral Sex