The answer to your question depends on a couple
Semen is composed of sperm (male reproductive
cells) and seminal fluid (sugar and liquid that
transport the sperm).
Vaginal fluid is primarily fluid discharged
from the cervix.
During sex these fluids are exchanged and do
not usually contain blood cells.
However they can contain other things that are
also found in the blood stream.
Viruses present in the blood stream can also be
found in semen and vaginal fluid. The one you've
probably heard most about is the HIV virus
which causes AIDS.
Other viruses in the blood stream can also be
transmitted from one person to another via semen
or vaginal fluid.Blood cells do not have to be
present in order for the virus to be
There are some circumstances which make it
likely that blood cells can also be exchanged
during sex. If one person has a sexually
transmitted infection (which might result in an
off-odor or off-color discharge) then the
increased irritation during sex can easily lead to
Increased inflammation at the site of the
infection also brings more blood cells to the
Another circumstance in which blood cells are
exchanged is during rough sex that leads to tears
in the skin or vaginal wall. Using a condom
will prevent (98% of the time) any cells from
being exchanged during sex except skin cells
in the area that the condom does not cover.