When Jennifer Aniston was shooting the movie We’re the Millers last year, she tried a product she liked so much that, as the familiar saying goes, she bought into the company. She’s now a co-owner and spokesperson for the premium haircare range Living Proof.

“For years and years I’ve been asked to endorse hair products and I’ve always said ‘no, no, no,’” says Aniston, who recently became an ambassador for natural cosmetics company Aveeno, but hadn’t leant her name to a brand since she fronted the ‘Because I’m worth it’ campaign for L’Oreal in the 90s. Why? She worried, she says, that “people would ask, ‘is this just another celebrity endorsement?’” and not trust her as a result.

“What caught my attention about Living Proof is the company’s unique approach to haircare – using scientific technologies to offer women actual proof in a bottle rather than hoping for results.”

OK, that’s the science bit. The fact is that for A-listers like Aniston, who are very protective of their public image, endorsing a hair or beauty product doesn’t just mean lending their name to it – they have to be sure it actually works. While some Hollywood stars continue to opt for the more traditional role of brand ambassador for cosmetics houses, including Julia Roberts (LancÔme), Emma Stone (Revlon) and Gwyneth Paltrow (Max Factor), there’s a growing trend for A-listers to become involved and hands-on with actually creating the ranges they’re saying they use.

Among them is actress Katie Holmes. Already the face of Bobbi Brown cosmetics, she recently joined forces with the celebrated make-up artist to create the Bobbi & Katie Collection, “the ultimate make-up line for today’s modern woman”.

The range includes a mini-brush set and a face palette inspired by one of Katie’s own favourite journals and her “classic design sensibility”.

“I’m really excited to be a part of this,” said Holmes, who can be found modelling Brown’s limited-edition Nude Glow collection. It’s an enduring partnership that clearly works for both sides.

Meanwhile, international superstar Rihanna has collaborated with Mac cosmetics on her RiRi Hearts range (including a Love, Rihanna soft golden brown bronzing powder and Bad Girl RiRi matte taupey nude lipstick).

“Being creative is something 
I love,” she says of the products, which are encased in white-pearl packaging with rose-gold detailing and her signature. “I’ve been using Mac on tour for so long it was a natural fit for me.” Rihanna is also the face of the cosmetics line’s Viva Glam range, while Fashion Police 
co-host Kelly Osbourne and her mother Sharon recently announced they would also be working with Mac on a range launching in June.

While it’s unlikely they’re putting on white coats and going into the lab or sourcing ingredients from around the world, in this social media savvy age, A-listers are ensuring they’re involved in the development and marketing of any product or brand they’re associated with. So why does celebrity endorsement still matter, what do we as consumers get out of it, and how can it make or break the commercial success of a brand?

“Celebrity-endorsed beauty products are very popular in the UAE,” says celebrity make-up artist and blogger Najla Kaddour. “The women here are very fashionable and want to look beautiful. Whenever a celebrity collaborates with a beauty brand many women feel the need to buy the products because they look up to them. By buying and using the same products as celebrities, they can recreate the look, which makes them feel and look beautiful. For example, Rihanna’s collaboration with Mac means every woman has the opportunity to wear the exact same lipsticks as Rihanna. And if she’s wearing it, it must be good, right?”

So not only are we hoping that a little bit of stardust will somehow rub off on us when we apply that eyeshadow, lipstick or bronzer, we’re also buying into the trust we have placed in the celebrity (or their public persona, at least) – 
if they say it works, it must work.

“We buy celebrity-endorsed cosmetics because it produces 
a feeling of gratification,” says beauty expert, author and beauty coach Antonia Mariconda. “It’s aspirational. But the majority of us will only buy beauty products endorsed by a celebrity if we believe the celebrity actually uses it.

“People believe, for example, that David Beckham might use a Gillette razor to stay groomed; but we take more convincing that a celebrity or film star uses a relatively inexpensive face cream or lipstick when we know they have the top colourists and make-up artists at their disposal.”

Kaddour agrees. “Celebrities have 
a huge fan base and millions of followers on social media. Usually whenever a big artist collaborates with a big brand it sells out immediately. If celebrities support 
a brand, that usually means they believe in the product, which leads to the customer believing in it as well.”

The most successful partnerships are the ones where the celebrity accurately reflects the essence of the brand – for example, Chanel and Nicole Kidman.

However, not all celebrity endorsements are successful: it’s also important that a brand isn’t overshadowed by whatever may be going on in the star’s personal life. “It’s crucial that the celebrity has 
a positive perception in the minds 
of the public,” says Mariconda.

“For example, Nicole Scherzinger is hugely popular and has amazing hair, so people are more likely to buy the shampoo she endorses [Clairol’s Herbal Essences]; however, when Britney Spears partnered with Elizabeth Arden on her Midnight Fantasy fragrance in 2007, events in her personal life affected sales. How a celebrity is viewed by the public can make or break a product.”

One thing’s for certain: next time you pop to a beauty counter for the latest celebrity-endorsed lipstick, you won’t be alone. A recent survey by hollywoodlife.com found that 
72.5 per cent of women would buy the Bobbi & Katie collection, and it sold out; and last June Rihanna’s latest lipstick for Mac sold out three hours after going on sale.