Hair extension horrors! They're how celebrities cheat their way to enviably swishy manes. But they can go humiliatingly wrong...

Perfectly groomed celebrities, their pictures splashed across glossy magazines, can leave ordinary mortals feeling a little flat by comparison. 

What’s their secret, you can’t help but wonder? 

How are their smiles so achingly bright, their hair so impossibly full and bouncy?

The answer to one of those questions, at least, has been provided by Cheryl Fernandez-Versini, who was spotted earlier this month with some rather obvious hair extensions. 

She’s one of many celebrities who need a little help with their tresses, although few would ever admit it.

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Blowing in the wind: Cheryl Fernandez-Versini's lighter coloured weave was revealed during gusty weather

It’s hardly a new idea — the business of adding hair to your head, whether fake or human, has been booming since Ancient Egyptian times. Yet, keeping them subtle is quite a challenge. Here, Femail investigates the pitfalls of the secret world of hair extensions.

WHO'S USING THEM? 

‘Everyone loves Cheryl’s hair, and thousands of women are choosing to have extensions,’ says Karl Warner, extensions specialist at celebrity salon Electric Hair, in London’s Marylebone.

‘She illustrates how much women want healthy, bouncy, shiny and — most importantly — thick hair. Unless you have been blessed genetically, extensions are literally the only way to get this Hollywood look.

‘Barely anyone has naturally thick, long hair. These days, extensions are accessible to everyone — and they work.’

There has also been a sea change in our approach to hair extensions. ‘They used to be a bit “glamour model”,’ says Karl. ‘Women now want a sophisticated and discreet look, frequently asking for just a few extra strands to be woven in. This adds volume as well as length.’

Karl points out that Cheryl’s hair mishap, when her extensions were revealed by an unfortunate gust of wind, could have happened to any celebrity, so rare is it for A-listers to go natural.

Lying flat, no one would have guessed. ‘The extensions blend impeccably into her colour, creating a highly fashionable, highlighted look,’ he says.

HOW DO THEY WORK? 

A common form of extension is the weave, a long strip of hair tied at the top with very fine, strong thread. This can simply be clipped into the hair with grips, for a temporary fix — although this type often slips out and is easier to spot than permanent ones.

Take Liz Hurley’s extensions, which were revealed when a breeze parted her hair. The broad strip of extensions did not sit flush with her roots, suggesting it had been clipped in rather than attached.

Revealing her hair secrets: Elizabeth Hurley's clipped-in weave is exposed by the wind

Alternatively, a weave can be sewn directly to a layer of your hair. ‘This can look a bit lumpy on fine hair,’ says Karl.

In a third method, the LA weave, tiny metal loops known as ‘micro-rings’ are sewn along the top of a strip of hair strands. Each micro-ring is slipped around a few strands of your natural hair. Finally, the metal rings are crushed with a device like pliers, flattening them and clamping them onto your hair.

‘The weave strip goes all the way round the head in a gentle curve from above each ear,’ says Karl. ‘The hair lies flat and looks natural.’

The worst faux pas occur when there isn’t enough hair at the crown to hide a weave, leaving a broad strip on display. Britney Spears, whose natural hair was too short to cover her extensions, was left exposed for this reason.

 Many shades of blonde: Britney Spears's weaves are visible beneath her naturally short tresses

Hotels heiress Paris Hilton clearly showed off her weave when she unwisely pulled her top layer into a high ponytail. There are also the more traditional single-strand extensions. 

Each strand consists of a bunch of about 100 individual hairs which is fastened on to your own locks beneath the top layer of your hair, using a glue containing keratin, a natural component of hair.

Karl explains that a full head of hair will require 150 to 200 strand extensions between 16in and 24in long. The glue is melted with a special heat gun, then hardens as it dries, sticking your hair and the extension together.

Other methods include attaching extensions with special tape. 

Fans include singer Ellie Goulding. Yet the individual strand method has some risk, as shown by former wild child actress Lindsay Lohan, who appeared to have developed a thin patch at the back of her head, suggesting the natural hair had been weighed due to repeated, over-use: hair needs to be ‘rested’ or it will fall out.

HAIR FROM CHINA 

Exposed: Paris Hilton's all-too-obvious weave was put on show when she tied her hair into a high ponytail

The best hair for extensions is human. 

It’s said that just under £43 million worth of human hair entered the UK in 2013. It’s sourced from all over the world, particularly China and Russia. 

Always ask your stylist about the provenance of the hair and whether it has been ethically sourced. There are still many stories about women in labour camps being forced to have their heads shaved.

The most prized hair is a type called Remi, made from the highest quality human hair. In these locks, all the hair cuticles lie flat in the same direction, so the extension is smooth and sleek.

THE £1,000 BILL 

Prices vary widely: top London salons can charge up £1,000 for a full head of long, thick extensions.

‘If you choose the most expensive real hair — which is very blonde — and want it long and thick, that’s around 200 strands, for which we’d charge about £900,’ says Karl.

A mid-range salon might charge £300 or £400; while synthetic clip-on extensions cost as little as £5.

‘You don’t have to have real hair,’ points out Yanike Palmer, Product Development Manager for international company Sleek Hair Extensions. ‘It depends on your expectations. There are sew-in synthetic weaves available.

‘Or if you’re going to a party, just buy a couple of packets of clip-on hair for about £10 each.’

Many salons will give you a hand with clip-ons if you’re stuck.

HOW TO BLEND THEM 

Hair extensions can be an easy way to add a bit of colour, creating highlights or contrasting sections without damaging your hair with chemicals. But if you experiment with different coloured extensions, they must be applied carefully.

The top layer should perfectly match your hair, before bringing in hair colour effects such as balayage (highlights to look like natural sunkissed blonde) or ombre (colour applied only on the ends).

‘Good-quality extensions ought to blend in with the root colour of your natural hair,’ says Karl.

That’s something Abbey Clancy got wrong when she revealed a blonde streak of extensions against her darker hair at the Hunger Games premiere last month.

DO THEY EVER LAST? 

No clip-on hair, however well applied, will last more than a couple of days. A synthetic weave will last about four weeks, while a high-end set of real human hair extensions might look sleek for three months.

After that, your own hair will have grown, so the extensions will be much lower down on the hair shaft and start to look messy.

Unsightly: Very long and heavy individual hair extensions have tugged at former wild child actress Lindsay Lohan's natural root, causing a bald patch in the middle of her scalp 

If the extension was attached using micro-rings, these can be taken out and the strands of hair repositioned. ‘We offer an hour-long service which costs £150. I move the extensions up the hair shaft so it looks newly done,’ says Juan Luis Gosp De Vicente, extensions specialist at Trevor Sorbie.

Yanike points out that Cheryl’s extensions seem to have slipped. ‘It appears they might have been clipped in, then slipped down. There needs to be enough hair to cover the extensions, so she needed to backcomb to create volume.’

MAKING THEM SHINE 

All the experts agree that it’s lack of attention that prevents quality hair extensions lasting longer. ‘I cannot stress the importance of aftercare enough,’ says Yanike.

Always use cleaning products recommended by your stylist. Most important is an oil — remember, an extension is not moisturised by natural oils like your own hair, so you need to rub on a few drops of almond, coconut or silicone oil when the hair is wet, to keep them soft.

Use a decent soft bristle brush —most stylists recommend the Tangle Teezer (£10.99, johnlewis.com), a brilliant brush for knots.

‘Look after your own hair, too,’ says Anabel Kingsley, Trichologist and Hair Care Expert at Philip Kingsley. ‘It’s vital to exfoliate dead skin cells, which collect on the scalp, by shampooing well.’

THE RISK OF BALDING 

We’ve all seen pictures of celebrities with bald patches thanks to years of heavy extensions. So, could your vanity leave your hair in a worse state than it was before?

‘I wouldn’t recommend extensions as a permanent solution to fine hair,’ says Anabel. ‘However high quality they may be, hair is still being pulled down by gravity.’

She recommends saving extensions for an event such as a big party or wedding. ‘If you have thinning hair, investigate the underlying problem — it could be diet, stress or low iron levels,’ she adds.