There are so many things to love about the festive season, not least the opportunity it affords to put on a full party face. On a day-to-day basis my look is pared back: a swipe of mascara and lip balm and that’s it, but if ever there was a reason to break out the glitter eyeliner, or that Hollywood starlet lipstick, the party season is it. Never mind that it might not have seen the light of day in months, or that it was a gift from an old flame, whom I haven’t seen in close to a decade – I’ve never thought of replacing it.

That was until I was asked by my colleagues if I wouldn’t mind handing over my make-up, for analysis, oh and I probably wouldn’t be getting it back. It seemed cruel, but they had their reasons. Scientists at Aston University studied almost 500 lipsticks, eyeliners, mascaras and beauty blenders and found enough superbugs to wipe out an army, with nine in 10 used make-up products harbouring potentially lethal pathogens. Poor bathroom habits and using products past their expiry dates were likely to blame.

[Make-up ideas, inspired by these 4 celebrity style icons]

The thorny issue of expiry dates doesn’t bode well with the envelope of treasures I’ve unearthed for Dr Amreen Bashir, the study’s lead microbiologist, who will be testing my make-up. The packet contains one lipstick, which was a Christmas gift from a boyfriend circa 2014. Never mind that its glossy black and gold packaging is now as battered as an old dustbin, the vampy pout it imparts still elicits a nostalgic flashback to that romance. Exhibit number two is a liquid liner bought with my daughter for the first of the 16th birthday parties. It was so eye-wateringly expensive that we decided to share it.

Then there’s the pretty pink eyeshadow, bought in Paris for my daughter Edie, 19, on our first girlie trip, eight years back. It should probably be in quarantine, but I just can’t bear to part with it. Then there’s the lash curl, a present from my son. It has lost its eye-catching yellow cap and almost dried to a crisp but the thought of a 15-year-old boy buying make-up for his mum, and not just any make-up, the It mascara of the moment – who could possibly chuck that?

Just as hard to part with, for purely practical reasons, is my Urban Decay Heavy Metal Glitter Eyeliner, a tip-off from my genius beauty editor friend, which is my party go-to and never fails to elicit a compliment. And finally, I’ve thrown in a make-up brush and one of my daughter’s beauty blenders. Blenders are the lavatory brushes of the beauty world, apparently – 92 per cent were found to be carrying some kind of germ in Dr Bashir’s study.

I’m a little terrified of offering up my make-up for analysis, but also intrigued to see what will turn up.

When we speak on the phone a week later Dr Bashir is sympathetic. ‘These things are very expensive, often £30 or £40 for a small pot. So you’re unlikely to throw it away if you’ve hardly used it, but once something is open the preservatives will only work for a limited amount of time – you can’t keep anything indefinitely,’ she warns. ‘It’s like the sell-by date on food. Once you are past the expiry date, bacteria will grow.’ The symbol to look for is a small pot with an open lid; it will have a number on it, followed by an M that stands for months, which indicates how long the product will last after it is opened.

Until now, I’ve never noticed any problems. Does it really matter if our make-up is crawling with bugs?

‘These pathogens are OK if you are hardy, but if your immune system is compromised in any way, if they enter your body, they could grow and proliferate and could lead to blood-borne poisoning and sepsis [a life-threatening infection],’ says Dr Bashir. ‘The other thing to remember is that these bacteria are in our natural environment. In low numbers that will not cause you harm, but given the opportunity to feed on nutrients, such as those in make-up, the number can grow to a level that can harm us.’ Lesser infections caused by staphylococcus (staph) bacteria include impetigo, a contagious rash that can envelop face and body, and conjunctivitis.

Serious infections are more likely when there is a small break in the skin, as when someone has acne or eczema. ‘The default position for a lot of people with these skin conditions is to layer on foundation to cover it, but if there’s a break in the skin this will allow infections deep into the body which can be life-threatening,’ says Dr Bashir, adding, ‘some forms of the staph bacteria, such as MRSA, don’t respond to antibiotics’.

The fact that Edie and I occasionally share make-up is a cause for concern. ‘Even though you are related, bacteria are unique to each person,’ warns Dr Bashir. ‘You’re effectively transferring one person’s flora to another person, which can potentially cause harm.’ She cites the young Australian mother, Jo Gilchrist, who was left partially paralysed after borrowing a make-up brush from a friend and contracting an antibiotic-resistant staph infection.

So how did my party slap fare? Extraordinarily, given its age, it gets a near-clean bill of health, with little or no bacteria to speak of, apart from on the shared liquid liner. The fact I use my party make-up infrequently has likely saved it from the bugs. My daughter’s make-up brush and blender have fared less well, and while there are no superbugs, they are teeming with a huge number of bacteria. ‘More than you’d expect on a lavatory seat.’

This isn’t a problem unless she shares her make-up with friends. ‘We found a lot of staph on there, but nothing pathogenic,’ says Dr Bashir. ‘And we didn’t find E. coli, which is great. It means you’re both good, safe make-up users.’

In contrast, Dr Bashir found E. coli on 27 per cent of the beauty blenders in her study. ‘It is an indicator organism of faecal matter, which tells us someone hasn’t washed their hands, or has dropped it on the floor,’ says Dr Bashir, adding that make-up can also be contaminated through the air. ‘When you flush the lavatory, whatever was in the loo can go around the room in particles, through aerosolisation.’ Eugh. Neither Edie or I do our make-up in the bathroom, but just to be sure, I run through safe practices with Dr Bashir.

The five-second rule does not apply to make-up: if you do drop a blender, wash it. Dr Bashir suggests washing blenders and all brushes weekly in hot soapy water or with a mild shampoo. ‘Press it against the soap until all the gunk comes out.’ And ensure that it is thoroughly dry before you reuse it, to limit the number of bacteria.

And, if I ever use Edie’s lipstick – not that I would dare to now – or she borrows mine, Dr Bashir suggests taking a knife to it and slicing off the end. In fact, any lipstick used regularly could benefit from a trim every two weeks, says Dr Bashir. ‘Or clean it with isopropanol or rubbing alcohol.’

The liquid liner is harbouring bacteria, one known as bacillus cereus, which is linked to food poisoning. All that double-dipping causes bacteria to run rife.

But can we really be blamed for using old products, when the use-by dates are so small, you practically need a microscope to read them and they almost instantly rub off? Dr Bashir agrees that cosmetic companies could be doing more to raise awareness with clearer expiry dates.

As for me, I have conducted a brutal cull of all of my out-of-date products.

Average make-up expiration dates

Eyeliner: a pencil, six months to a year Liquid eyeliner: six to eight months

Mascara: three to six months

Blush, eyeshadow and other powder cosmetics: 18 months

Foundation: a water-based product will last up to a year, oil-based will last up to 18 months

Lipstick: 12-18 months

The Daily Telegraph