What does paradise smell like?

At Puli Hotel and Spa the olfactory stamp is a beneficial blend of orange, lemon, peppermint and pine oil.

As for Le Meriden, a luxury collection in the group founded by Air France in 1972, its scent LM01 TM was inspired by the book Le Petit Prince, on the premise that they share a connection with France and aeroplanes.

The scent, formulated by a niche fragrance store, Le Labo, in New York, smells of "old books, old paper, leather and the wooden shelves" of a library, and has helped the hotel become more "distinguished" after it was taken over by Starwood in 2005 and in need of a clearer identity to communicate with guests.

At the exclusive St Regis, the lobby is scented with the aroma of roses and sweet peas, harking back to the home of the Astors, the founding family. While the flowers paid homage to Brooke Astor, the tinge of tobacco in the air reminds guests of Vincent Astor.

At Puli Hotel and Spa, the first luxury hotel designed as an urban resort in Shanghai, the olfactory stamp is a beneficial blend of orange, lemon, peppermint and pine oil.

Invisible though they may be, these signature scents are not necessarily subliminal, as believed by many. But it is backed by science, as neuropsychologists find that pleasant fragrances can trigger positive memories and sometimes, nostalgia.

Some guests not only notice the scents, but they want to take it away with them.

"We have developed and packaged the scent into a room spray, diffuser and candle for guests to buy for themselves or as gifts," says Ilona Yim, director of public relations at Shangri-La International Hotel Management.

At the Shangri-La Hotel Pudong in Shanghai, about 70 bottles of the Essence of Shangri-La reed diffuser is sold every month, at 480 yuan for 200 ml. At Langham Xintiandi in downtown Shanghai, the signature ginger flower scent is the most sought-after product at its gift shop and often sold out.

But there are also hotels that choose to go fragrance-free.

"For one thing, we think the choice, or preference, of scents is a very subjective and private thing," says Ma Yunzhi, marketing manager of Park Hyatt Shanghai.

The tallest hotel in Shanghai, at the top of the 492-meter World Financial Center, has a long list of reasons for greeting customers at its 87th floor lobby with only fresh air. Park Hyatt cites environment protection, lowering the risk of allergies, and perhaps most importantly, keeping its "low-profile" character.