From the wiki page:

Toulouse-Lautrec became fascinated by the nightlife in Paris, particularly sex workers. Through the 1890s, he spent more and more time painting everyday scenes of life in the official brothels, the maisons closes. In 1892, he was commissioned to produce paintings for the salon at a brothel on the rue d’Ambroise. He spent time observing the brothel, its residents and visitors, while they worked and at quieter moments, and made sixteen portraits of the sex workers. These paintings demonstrate a close and intimate observation and compassion towards the subjects, without any sense of sensationalism or voyeurism.