Dear Hearted Girl,
Yes, it is true. In fact, a man can smell when a woman is ovulating thanks to something called “female pheromones”, in combination with the role of testosterone. Olfactory clues from women who are on their ovulatory phase (i.e. their most fertile time) can make men more willing to have intercourse with them.
Various studies have confirmed that smells affect hormones, and subsequently the mating habits of animals, as odors emitted by females increase the testosterone levels of males, particularly during ovulation.
I hope this helps,
Best wishes
