Sperm cells in a condom. Computer artwork of sperm cells (red heads, blue tails) in the teat area of a condom (not to scale). Sperm cells (spermatazoa) are the male reproductive cells. They are formed in the testes and are released during ejaculation in a fluid called semen. A condom is a latex rubber sheath used as a barrier contraceptive to prevent the sperm cells entering the female reproductive tract. This prevents unplanned pregnancies, and also helps to prevent the spread of STDs (sexually transmitted diseases). The teat area of a condom is designed to contain the semen and to reduce the chances of the condom bursting.