With the aid of a glamorous wardrobe overhaul and glossy hair extensions, Kate Beckinsale was transformed from demure English rose to A-list starlet.

But after displaying a prominent bald patch during a recent shopping excursion, the 33-year-old actress may well be ruing certain aspects of her Hollywood makeover.

With her eyes hidden behind a pair of designer Aviator sunglasses, the London-born star stepped out in LA, where she has a home, wearing a short-sleeved grey jumper teamed with black minishorts and a pair of knee-high biker boots.

Looking suitably stylish from the front, it was only as she turned around - showing off a distinct bare patch below the crown in her hair -that things took a decided turn for the worse.

It is thought that the Pearl Harbor star, who is said to have been a fan of temporary hair extensions, may have acquired the patch as a result of this treatment.

Of course, assuming a cruel trick of the light is not to blame, Miss Beckinsale may be suffering from alopecia, the condition that caused TV presenter Gail Porter to lose all her hair in 2005.

Glen Lyons, Clinical Director at the Philip Kingsley Trichological Clinic in London, said: 'You don't get a single bald patch, or female pattern hair loss, from medication or extreme diet but diffused general hair shedding.

'So it is absolutely possible that alopecia, a big reflection of stress, is the cause of this bald spot.

'Otherwise, it is possible that hair extensions are to blame. Although techniques have improved, the potential damage caused by traction - the pulling of the attachment from the glue - remains. Some degree of traction is unavoidable.

'Potentially you can cause damage, with breakage from the hair shaft. It could break within one to two centimetres of the scalp - the hair can still grow but it would break off where the extension was attached to the natural hair.

'But really, a lot of it is in the hands of the technician and obviously some are better than others.'

The Oxford-educated actress, the daughter of former Porridge Richard Beckinsale, is by no means the first celebrity to be spotted with thinning hair, the result of poorly maintained extensions.

Victoria Beckham, Christina Aguilera and Nancy Dell'Olio have all sported questionable bald patches in recent times, while former

Friends star Jennifer Aniston has claimed that her famous locks were ruined by hair extensions.

Despite such negative publicity - and a treatment cost of at least ¡ê600 per session - demand for hair extensions has doubled in the past three years.

Made from fibre or real hair - usually imported from Russia or Poland - they are either woven into the roots of the hair or simply glued on.

Hair extensions are often added to the back of the hair which is why this is the likeliest spot for bald patches.