People having an anaphylaxis attack have to worry about secondary reactions, like expiration dates and having the wherewithal to auto-inject their thigh.

Rosemary thought she had done everything right.

While traveling in Costa Rica, it would be hard to communicate about her food allergies to milk, eggs, peanuts, beef, lamb, and crab, but her boyfriend spoke Spanish fluently and could talk to waiters for her.

Plus, she had packed Benadryl and an EpiPen just in case.

One night after dinner, however, Rosemary began to feel funny. By the time she and her boyfriend got to their hostel, her face was swollen and flushed.

“I took some Benadryl and hoped it would just go away. An allergic reaction was not what we needed that week and I didn’t want to ruin the vacation,” she told Healthline.

But her symptoms worsened and soon she was struggling to breathe.

“I went for my EpiPen and injected it into my thigh,” Rosemary recalled.

Not much happened, so she checked the label. Sure enough, it had expired.

Rosemary hadn’t thought to refill her prescription because at home she lived just five minutes away from an emergency room.

“If I had a reaction I could go there and not worry about spending hundreds of dollars on a new EpiPen to have ‘just in case.’ I took that medical access for granted,” she said.

Read more: The long, strange history of the EpiPen »

Access to EpiPens is something that few people can now take for granted, even — or especially — in the United States.

The price of the life-saving auto-injector has increased by 600 percent since the pharmaceutical company Mylan acquired it in 2007.

Over the same time period, many customers have seen their health insurance premiums go up and their prescription coverage change from flat copays to pricey deductibles.

That means a lot of people were suddenly responsible for paying the full price of the EpiPen. Like Rosemary, some responded by hanging onto expired EpiPens, while others put off filling their prescriptions.

That’s a dangerous gamble. A severe allergic reaction can lead to life-threatening anaphylaxis, a condition in which blood pressure plummets and airways close off.

“I always tell people the first three treatments for anaphylaxis are epinephrine, epinephrine, epinephrine,” Dr. Anthony Montanaro, an allergist at Oregon Health and Science University, told Healthline.

When people die from anaphylaxis, it’s usually because they don’t get epinephrine on time. That might happen even if they do have a working EpiPen on hand.

A study published last year found that of 102 people assigned a dummy EpiPen, only 84 percent used it correctly. Many patients didn’t hold it in place for 10 seconds after injection. Others didn’t jam it hard enough or held it the wrong way, which can lead to shooting epinephrine into the thumb or losing the medication all together.

The EpiPen is meant to deliver medicine right into the muscle so that it can be absorbed into the blood stream as quickly as possible. For patients who don’t deliver it correctly or for whom the needle is too short to reach the muscle, the EpiPen won’t do its job properly.

It’s this kind of confusion that an alternative auto-injector, Auvi-Q, meant to solve with voice commands that talked a patient through its deployment. But that device was recalled last year.

Read more: Why parents want all ambulances to carry EpiPens »

Many patients hesitate to use their EpiPens, which Montanaro says is the “absolutely wrong thing” to do.

In general, there’s no real reason for a person prescribed an EpiPen to avoid using it during an allergic reaction. With such a low dose, risk of side effects are low.

That doesn’t mean it’s fun getting a shot of epinephrine, which is just another name for adrenaline.

“I’ve given myself an EpiPen just to see what it was like and it’s not a comfortable experience,” Montanaro said. “You feel totally uncontrolled, you feel anxious, and your heart races.”

Once injected, epinephrine works quickly to raise blood pressure and open airways.

However, one dose may not be enough for everyone.

Up to 20 percent of people experiencing anaphylaxis will have what’s known as a biphasic reaction, in which they are wracked with another attack hours after the first.

And reactions can vary with time and triggers, meaning that someone whose attack subsided after one shot in the past might find themselves in the 20 percent category the next time.

That’s why doctors strongly advise that anyone experiencing an anaphylactic reaction — which Montanaro defines for his patients as any reaction that affects more than just the skin — seek emergency treatment after using the EpiPen, even if they feel better.

At the emergency room, they can be monitored for further attacks and given additional epinephrine, as well as steroids like Prednisone and antihistamines to help with other symptoms.

Read more: Rising cost of EpiPens forcing some allergy sufferers to switch to syringes »

Rosemary was saved when her boyfriend found an off-duty doctor who opened his clinic for them.

“After proper epinephrine and IV steroids and close monitoring I was in the clear,” she said.

Now when she travels, she notes the location of the nearest hospital and pays for an international cell phone.

But ultimately, her safety depends on access to epinephrine. The sky-high price of the EpiPen is, for her, not just a symbol of corporate greed but something that actually put her life at risk.

“I hope someday soon the FDA approves a generic version, or the drug company decides to lower the price. The last thing someone needs when their throat is closing up is to worry about hundreds of dollars for a trip to the emergency room and hundreds more to replace the EpiPen,” she said.

“For people with severe allergies this is just the reality, and has been for years,” she added “The EpiPen price has been a hot topic lately, but for people like me, we have been dealing with it for years.”