A bad penny? New coins and nickel allergy
Tests suggest people with a nickel allergy can be at increased risk when handling the UK's new 5p and 10p coins.
The coins, introduced in January 2012, caused a complete shake-up in the world of small change.
Instead of the copper-nickel alloy that's been weighing down our pockets since 1947, new 5p and 10p pieces will be made from steel and coated with a layer of nickel.
To the untrained eye, there's very little difference. They've got the same silver shine and the same jangle.
But for the 10% of the population who suffer from a nickel allergy, they could feel very different indeed.
Concerned dermatologists wrote to the British Medical Journal after the coins were released to call for a proper assessment of the health risks.
Now a study in Sweden has answered that call and suggests UK citizens are being "unnecessarily exposed" to higher levels of nickel on their skin.
Taking the shine off
Doctors refer to nickel allergy as an "allergic contact dermatitis", which means the skin is only affected if it comes into contact with an object containing nickel.
Although some people may have a genetic predisposition to nickel sensitisation, for most people it's triggered by long-term environmental exposure.
"It's like a switch," says Dr Anneli Julander, the study's lead author.
"Someone might be exposed to nickel every day without a problem and then one day it just flips over for you."
Allergy UK deputy chief executive Lindsey McManus, who developed a nickel allergy 30 years ago, told BBC News: "I have reactions to inexpensive jewellery, bra clasps and sometimes watch straps.
"I only have to wear cheap earrings for about 20 minutes before my ears start itching madly, swelling and weeping. And I'm at the minor end of the spectrum. For some people it can be much worse."
The condition can be controlled by avoiding objects made with nickel or nickel alloys. But that's easier said than done, with everything from jewellery to jean studs, and door handles to keys, containing the metal.
And for most people, the sensitisation to nickel is lifelong.
"The problem is that once you have a nickel allergy, you can never go back," says Dr Julander.
Counting the cost
Since the 1940s, all "silver" coins have been made from an alloy of 75% copper and 25% nickel.
But with rising copper prices, the Treasury and the Royal Mint realised they could save £7m to £8m every year by swapping to nickel-plated steel for 5p and 10p pieces.
"Independent tests have been conducted [on the new coins] by three accredited laboratories using internationally recognised tests for nickel release," says Cheryl Morgan from the Royal Mint.
"We are satisfied that there is no increased risk of people developing a nickel allergy by handling the coins."
But an international team of researchers says the tests are flawed.
"The standard test involves putting coins in a pot of artificial sweat for a week. You then measure how much nickel is released from the coin, which obviously doesn't resemble how we handle coins in everyday life," says Dr Anneli Julander, who works at the Karolinska Institute in Sweden.
To put things right, Julander and her colleagues asked six volunteers to spend an hour moving the new nickel-plated 5p and 10p coins between two boxes. They then measured the traces of nickel left on their skin.
"We found that the amount of nickel was four times higher after handling the nickel-plated coins compared with the old copper-nickel ones," says Dr Julander.
A bad penny?
Ironically, a closer look at the composition of the new coins shows that they actually contain less nickel than the older ones (see box).
But despite being only 6% nickel, 100% of it is concentrated on the surface of the coin - the same surface that will come into contact with people's hands.
Cashiers and bank clerks are most likely to be affected, although there is no consistent evidence that nickel-plated coins actually cause nickel allergy.
However there is plenty of anecdotal evidence that coins can aggravate the condition.
Allergy UK say a common example is men who carry coins in their pockets, only to find they have sore and itchy skin on their thighs as a result.
Rubbing up the wrong way?
Nickel-plated coins have been used around the world for nearly 60 years, so it's unlikely that the UK is on the brink of a massive health crisis.
But even so, Sweden has announced that it will stop producing any nickel-containing coins from 2015, stating that the metal posed "unacceptable risks" to health.
So what does the Royal Mint make of it?
"The Royal Mint is aware that some individuals do suffer from nickel contact dermatitis, and whilst nickel is present in a number of other materials, we are looking to work with bodies who specialise in this area," says the Royal Mint's Cheryl Morgan.
However despite the latest findings, it does not expect to have to change the coins at any time in the foreseeable future.
"We remain confident that there is no greater public health risk from the new coins than there has been from use of existing [copper-nickel] coins."