The final verse of Tehillim (150:6) declares, "Kol Ha’neshama Tehalel Kah" – "Every soul shall give praise to G-d." The Gemara interprets this to mean that one must recite a Beracha over an experience which brings enjoyment specifically to the Neshama (soul) – namely, the enjoyment of fragrance. This is the source of the special Beracha which is required when one smells a pleasing fragrance, a Beracha called Birkat Ha’re’ah.
One recites this Beracha before smelling the fragrance. The Sages did not institute a Beracha to be recited after smelling a fragrance (like we recite after eating), because the enjoyment of fragrance is slight and brief, and so it does not warrant a Beracha Aharona.
When one smells something which grows on trees, he recites the Beracha of "Boreh Aseh Besamim," and when smelling something which grows from the ground, he recites "Boreh Asbeh Besamim." Over fragrances from other sources, one recites "Boreh Mineh Besamim."
The Poskim addressed the question as to whether one must recite a Beracha before smelling synthetic perfumes, which are made from chemicals that are mixed together to produce a fragrance. The Gemara spoke only of natural sources of fragrance, such as herbs and spices, and the question thus arises as to whether this Beracha is restricted to items which naturally emit a fragrant scent, or even to synthetic sources of fragrance.
A number of Poskim, including Rav Shlomo Zalman Auerbach (Jerusalem, 1910-1995), maintained that since each chemical on its own is not fragrant, and the scent is produced only by combining them together, no Beracha is recited over synthetic perfume. Hacham Ovadia Yosef, however, in Hazon Ovadia – Berachot, disagrees. He notes that one of the fragrant products mentioned by the Gemara is "Mor," or musk, which, according to some views, was produced from blood taken from an animal’s neck, and, according to others, from an animal’s sweat. Either way, Hacham Ovadia writes, the main ingredient of musk clearly did not have a fragrant scent on its own, and its fragrance was produced by mixing it with other ingredients. This demonstrates that a Beracha is required even over fragrant products made from ingredients which do not have a pleasing smell independently.
Hacham David Yosef, Hacham Ovadia’s son, writes in Halacha Berura that when he spoke with his father about this issue, his father retracted the ruling he wrote in Hazon Ovadia. Another scholar, however, claims to have been present during that conversation, and that Hacham Ovadia did not retract his ruling. Regardless, it is difficult to rely on reports of Hacham Ovadia’s decisions that run counter to what he wrote in his books when he was studying the topic at hand. Therefore, we follow the ruling in Hazon Ovadia, that one recites the Beracha of "Boreh Mineh Besamim" before smelling synthetic perfume.
It should be noted that this requirement applies even if one is given a sample of perfume in a perfumery. One recites the Beracha over a fragrance regardless of whether or not he owns the source of the fragrance that he smells, and so if one is at a perfumery and is given a sample to smell, he must recite the Beracha of "Boreh Mineh Besamim." One does not recite the Beracha right when he enters the perfumery, even though there is a fragrance in the air, because all the bottles are closed. In earlier generations, perfume shops would keep open bottles and bags of merchandise in the store, and so one would have to recite the Beracha immediately upon entering and smelling the herbs. Nowadays, however, all the perfume bottles are closed, and so one does not recite a Beracha until he is given actual perfume to smell.
Summary: Before smelling synthetic perfume, one recites the Beracha of "Boreh Mineh Besamim." If one goes into a perfumery, he does not recite a Beracha right when he walks in, even though the store has a fragrant smell, but he does recite a Beracha if he is given a sample of perfume to smell.