When all the Students are in their fifth year they learn about Amorentia.
Amorentia is a love potion that creates an infatuation with a person or thing and is quite dangerous.
Amorentia does NOT create Love. It makes someone Obssess over an object of their Desire.
It is characterized by its mother-of-pearl sheen and swirling smoke that comes off the potion when brewed correctly. It also smells unique to each person according to things/people/places they love. These things/people/places don't necessarily have to be romantic interests. They can be things that make the person feel comfortable and at home, which does often translate into their romantic feelings.
Professor Baddock, the potions Master, always has her students study the potion in class. The next more than a few chapters are what I think they would smell in the Amorentia.