Health experts have warned women using lash serums that promise longer, darker lashes that the trending beauty product could also cost them their eye-colour. 

For those avoiding the expense of eyelash extensions, eyelash serums that promote hassle-free growth may seem like a safer, less expensive option.

But experts warn many of these products contain powerful pharmaceutical drugs that could cause burning, irritation and even permanently change a person's eye colour from blue to brown. 

It comes as lash serums have taken the beauty world by storm, promising darker, longer and fuller lashes at home. 

Over two decades ago a type of prostaglandin analogues (PGAs)—called bimatoprost—was approved by officials to treat glaucoma and ocular hypertension—eye conditions that cause pressure to build up inside the eye, eventually leading to vision loss. 

As well as treating the conditions with less side effects than earlier treatments, doctors noticed that patients eyelashes were also growing longer, thicker and darker.

Whilst it is not yet fully understood how the drug stimulates lash growth, researchers have speculated that it extends the active growth phase, where lashes grow to their full length fuelled by blood supply from the root of the hair follicle. 

In 2008 the drug—sold under the brand name Latisse—was approved by the US Food and Drug Administration (FDA) to treat eyelash hypotrichosis, an eye disease which affects the density of a patient's lashes. 

 Extensive research showed that the active ingredient was effective at making lashes longer after just 16 weeks of daily use, making it an attractive commodity for beauty product manufacturers. 

In the UK, whilst bimatoprost remains a prescription-only medication, manufacturers have harnessed the power of other PGAs to boost lash growth. 

However these powerful ingredients also come with serious cosmetic side effects including fat loss around the eyes, creating a hollow sunken look, unwanted hair growth where the serum spreads, drooping of the upper eyelid which may require surgery and permanent iris darkening—turning blue eyes brown.

A shocking investigation carried out by government officials revealed that almost one in four lash serums sold in the UK contain harmful PGAs which can cause skin darkening and irritation within just a few weeks of use.   

In the US, the FDA has previously issued urgent warnings stating that any cosmetic product containing these potentially harmful ingredients under growth claims should be treated as a drug and not a beauty product. 

Experts are now sounding the alarm stating that consumers may be unaware they are using these powerful ingredients that have been manufactured to mimic prescription-only treatments. 

Even if a products claims to be PGA-free, experts advise checking the ingredient list and staying away from anything ending in -'prost' to minimise the risk of redness and irritation. 

Instead they suggest opting for peptide-based alternatives, which work by boosting keratin to support lash growth—though these products too are not risk-free and there is very little evidence to suggest they actually work. 

Dr Mahmood, a New York based plastic surgeon, is just one of the many women who has fallen victim to the promise of darker, fuller lashes in a bottle. 

In a video posted to Instagram, she said: 'This is the one skincare product I would never recommend to any patient.' 

After using a lash serum for two months, Dr Mahmood said her lashes looked the best they ever had. 

But after a few days she noticed that one of her eyes was bulging out of her face and was significantly bigger than the other. 

After two MRI scans and further tests, doctors discovered that the lash serum had caused the muscles in her upper eyelid to thin, causing the area to droop. 

To compensate for this loss of vision, Dr Mahmood's other eye had started to bulge, resulting in two surgeries to restore her vision and lift her eyelid. 

'It's pretty clear prostaglandins are bad, especially when it comes to eyelash serums,' she told her 25,800 followers. 

'Even if your lashes look amazing for a couple of months or years, you are at very high risk of this happening. Please be careful.'