The potential for sexual service played a key role in the changing demand for slaves in medieval Europe. From the early Middle Ages on, the demand for male slaves declined while the market for female slaves rose. Although male and female slaves were vulnerable to sexual exploitation, only enslaved women's sexual service was tacitly sanctioned in the parts of Christian Europe where slavery was practiced. Their suitability for sexual service factored into their prices, in contrast to free domestic servants, whose wages were not influenced by their physical appearance. As a consequence of the common practice of slaves' sexual service in the cities where slavery was still practiced, the presence of children of slaves and masters in households gave rise to social pressures that diminished the demand for slaves within European households at the same time that slavery in European colonies was on the rise.