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When you hand your credit card to a cashier, you expect it to work. It’s a reasonable assumption, but plenty of consumers have had the experience of swiping a card multiple times to no avail. For some reason, the reader won’t recognize your card — it might happen once in a while, repeatedly at the same store or so often you have to get the card replaced.

Credit and debit cards have a shelf life, because the materials break down after years of use, and depending on how you use them, you could render your card useless before you’re due for a replacement. For example, some people say their cards were damaged by storing them next to their cellphones. There are also theories that static electricity can fry chip cards, but it’s hard to predict how your card will be affected by interactions with certain materials and devices, according to Barry Mosteller, director of research and development at CPI Card Group, a credit card manufacturer.

Your card’s potential for damage depends on a few things: how it’s made, where it’s stored, what it’s exposed to and chance — your credit card may be useless after you accidentally run it through the dryer, but if your friend makes the same mistake, her card may function just fine.


How Cards Stand Up to Damage

Most credit and debit cards in the United States use magnetic stripe technology — that brown or black strip on the back of your card contains tiny bar magnets arranged and encoded in such a way that a payment terminal reads it as your unique account.

There are two kinds of magnetic stripes, low coercivity (LoCo) and high coercivity (HiCo). Those distinctions relate to how many oersteds (the measurement unit of a magnetic field, abbreviated Oe) it takes to move the little magnets in the stripe. Mosteller said stripes are usually 300 Oe (LoCo), 2,750Oe or 4,000 Oe (both HiCo), with 2,750 Oe as the standard for payment cards.

Hotel cards and some loyalty cards are probably the only LoCo cards you’d have in your wallet, though the credit card industry used 300 Oe stripes in the 1990s. “They moved it over to 2,750 because of cards being demagnetized,” Mosteller said. Airline tickets used to be printed with a LoCo magnetic stripe, and you’ll still see these tickets from time to time, but it’s no longer common.

So what’s the difference between these cards that makes some more susceptible to magnetic fields? It has to do with the resin containing those tiny magnets. HiCo cards use a resin that’s more resistant to magnetism and heat, allowing everything to stay put, despite environmental disturbances.

Cards with chip-and-PIN and near-field communication (NFC) technology aren’t vulnerable to magnetism the same way magnetic stripes are, though those are unlikely to be ruined by your phone, a magnetic purse clasp or a refrigerator magnet.

Cards with chips are most likely to fail because of damage to the chip. When these cards were first manufactured, they were dying while being delivered to consumers, because the mail-sorting process was too rough on the chips, Mosteller said. Now cards are tested and built to withstand such abuse, but physical damage like bending the card (think of sitting on it or flexing it in your hand) remains the main risk to ruining those types of cards, Mosteller said.

Things That Could Ruin Your Card

If you’re concerned about keeping your phone next to your wallet or using a phone case with credit card storage, you don’t need to worry.

“If you have a HiCo stripe, the chance of a cellphone causing it to become demagnetized or unreadable is low,” Mosteller said.

Still, there are people who will tell you it happens. It’s possible, and people have experienced it.

“It depends how long the card was in contact with the phone — the face of the phone or the back of the phone? How well is the phone shielded? Did you receive any text messages while it was there?” There’s a lot of different variables that can have an effect,” Mosteller said. “On a HiCo stripe, I doubt it would be able to change it. On a LoCo stripe, yes, I think you can.”

Mosteller said he hasn’t personally tested a phone’s ability to demagnetize a card.

Magnetism is one way to potentially ruin a card — or cause jitter, as a disruption to the stripe is called — but heat can also cause problems, because it can soften the resin and allow the magnets to shift. Prolonged exposure to hazardous elements can also be problematic: Putting a card in a magnetic wallet may damage the card if it sits there long enough, but briefly putting the card in a magnetic field of the same strength won’t cause problems.

Then there’s card abuse, which can render all sorts cards useless. Friction can cause a magnetic stripe to wear off. Bending a card could crack a chip or break antennae used for NFC.

Payment cards are manufactured to last, but just like anything else we use on a daily basis, materials break down, and the way we use them has a large effect on how quickly that happens. Considering how common credit card fraud and data breaches are, you’ll probably have to replace a few of your cards before their expiration date, anyway.

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