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The CDC recommends against open mouth kissing with an HIV infected partner.
Although normal social contact such as kissing on the cheek, dry kisses, hugs, and handshakes are considered safe. Healthy unbroken skin is a good barrier to the virus.
Open-mouth kissing is considered a low-risk for transmission of HIV. Prolonged open mouth kissing with the potential to damage the lips or mouth could allow HIV to pass from an infected person to a partner by entering the mouth through cuts or sores present in the mouth.
CDC reference: http://www.cdc.gov/hiv/resources/qa/qa17.htm
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