What exactly does Jennifer Lopez smell like? The easy answer is money. The more complex one is "fruity freshness". At the launch of her debut perfume Glow in 2002, Lopez described the scent - which is infused with orange, grapefruit and vanilla - as "something that feels like you just came out of the shower and are the sexiest person in the world".
Perhaps this goes some way toward explaining the phenomenon of the celebrity fragrance: we just want to feel like our idols do after they've had a wash. Lopez's scent is credited with reigniting the Nineties vogue for superstar endorsement a decade ago and remains top of the perfume parade, bringing in an estimated NZ$1120 per hour for the curvaceous singer.
"The trend started back in 1991 when Elizabeth Taylor launched White Diamonds," explains Alessandra Steinherr, beauty director at Glamour magazine. "Many have come and gone since then and, of course, some are beyond hideous, while others are beautifully formulated and super popular. The good ones stand the test of time and the bad-quality ones tend to disappear."
In the past six months, Lady Gaga and Madonna have released their own fragrances, as have - rather lower down the celeb spectrum - Amy Childs (of The Only Way is Essex fame), X Factor runner-up Cher Lloyd and X Factor judge Tulisa Contostavlos. Clearly, there is a market for these products.
While the most popular overall - in terms of sales - remain Jennifer Lopez, Sarah Jessica Parker and Britney Spears, for many years Shh by Jade Goody was a bestseller. Launched in 2006 after Goody's stint on Big Brother, it sells today (three years after her death) as a collector's item on eBay.
"Fragrance has become increasingly part of everybody's daily dressing ritual," says Nicholas Gilbert, an olfactory expert based at London's top-end scent shop Les Senteurs. "The price point of celebrity fragrances seems to explain their popularity, however, you get what you pay for."
Most celebrity scents, he explains, use inexpensive fruity notes that are easily created and have widespread appeal among the nostrils of the masses. Sweet fruits, such as blackcurrants, strawberry and peach, are popular, as are "fantasy floral accords", invented concepts such as Red Vanilla Orchid, Dewy Lotus Flower, Coconut Orchid. Typically, celebrity scents combine fruity top notes with a floral heart and a cake-like base, with vanilla a common ingredient in many.
"Vanilla's comforting," Gilbert continues, "because it recalls the security of youth and nursery desserts, and is considered by some to be an aphrodisiac."
But celebrity fragrances tread a thin line between sex and sensuality: most of these products must be accessible to young fanbases with uneducated palettes, which is why so many of them smell so sickly sweet.
Pint-sized popstar Justin Bieber's fragrance Someday, launched in 2011 (the bottle sports a rubber floral effigy uncannily like that of Marc Jacobs's Lola) is a case in point: starting notes of mandarin, pear and berries ends in vanilla and soft musk. Wearing it for a day is like being trapped in a fudge kitchen.
"It explains a dream," Bieber told fans when it launched. "Someday I will drive a BMW. Someday I will be an astronaut."
When Bieber debuted his second perfume Girlfriend, British high-street chain The Perfume Shop reported selling one bottle a minute in the opening weekend, and a 132 per cent rise in online sales on the previous year. "All records were broken with the launch of Girlfriend," says the store's advertising manager Michelle D'Vaz. "It's safe to say Bieber fever is still a phenomenon."
Refreshingly, when reports last year surfaced that Lady Gaga would release a fragrance, the popstar said she wanted it to smell of "blood and semen". Since then however, she has had to row back a bit: the resultant scent, which came out last month, is merely based on the molecular structure of these two substances, and is structured by three accords - that is, three sets of notes which harmonise together. Belladonna; honey, saffron and apricot, and Tiger Orchid combine to make a singular perfume that is presented in a bottle that resembles an onyx egg clutched by an alien claw. Righto.
It might not sound very nice but what Lady Gaga, along with Madonna and reality-television star Kim Kardashian, has done is de-sweeten the celeb scent shelves. Madge's Truth or Dare is a traditional white floral scent undercut with amber, while Kardashian's mixes a difficult tuberose with sandalwood. They're very different from the other citrus celeb offerings: whatever one might think of buying into a brand because of the famous face behind it, these perfumes are noticeably more complex and less obviously wearable.
"I feel that fragrance houses need to take a risk to smash the mould of what a celebrity fragrance can be," says Gilbert. "The continued focus on group testing that the mainstream insists on using is leading to a homogenisation of the celebrity-fragrance market."
But Sarah Jessica Parker remains a cautionary tale. After releasing the bestselling Lovely in 2005 - capitalising on her profile at the end of the Sex and the City television series - she went on to create another product "Covet", a woody chocolate and lavender scent or fougère that she was heavily involved in building, and which proved simply too challenging for the common nose. It was swiftly discontinued.
"It's really down to how the celebrities approach the making of their perfume," says Steinherr. "How involved they are, how much it is a personal project or just a way to make a quick buck.
"Of course, initially the face of the fragrance is the determining factor as to whether the perfume sells, but the trick to getting longevity and repeat sales is to produce a great scent."
Ultimately, if it smells nice, most people will probably like it and part with their hard-earned cash for it. And others will do as a friend of mine does: decant her favourite fragrance - True Reflection by Kim Kardashian - into a Chanel No. 5 bottle so that her secret remains safe.