How to know if you're allergic to the COVID-19 vaccines by Moderna, Pfizer, or J&J

• Most people with severe allergies will not react to a COVID-19 vaccination.
• None of the shots from Moderna, Pfizer, and J&J contain preservatives. They have no eggs or latex in them.
• But they do include some other fatty substances, which, in rare cases, people can react to.

More than 44 million people across the US have been fully vaccinated against COVID-19 - that's about 13% of the country.

Just a very small fraction of those people, about 0.00045%, have had an allergic reaction. Their symptoms ranged from localized hives to wheezing or even life-threatening anaphylaxis.

"Fortunately, I'm not aware of anybody actually dying from getting the vaccine," Dr. Sanjeev Jain, a board-certified allergist, immunologist, and CEO of Columbia Allergy, told Insider.

Culprits at work in the three authorized vaccines, allergy-wise, seem to stem from a couple of ingredients: polyethylene glycol (PEG), and polysorbate. These are common additives, which help many products better maintain their moisture and stick together in a uniform way.

In the drug industry, these substances can be used to deliver fragile vaccines and medications in convenient formulations. They're also used in many other ways to make things run smoother, and can be found in everything from processed foods to colonoscopy prep solutions and face creams.

PEG and polysorbate are key ingredients in the COVID-19 vaccines authorized for use in the US (both Pfizer and Moderna's shots include PEG, while Johnson & Johnson's shot has polysorbate in it).

But Dr. Jain says, even if you do have an allergy to one of those vaccine ingredients, there are still ways to get vaccinated safely. In fact, if you've ever used a laxative, you may already have a pretty good indication of your risk.

What are the reactive ingredients in the COVID-19 vaccines by Pfizer, Moderna, and J&J?

While some people may want to pore over the ingredients listed in each vaccine, it's important for people with severe allergies to also have a basic understanding of what's not in any of these vaccines.

There are no preservatives, no eggs, and no latex. The ingredients to focus on are PEG and polysorbate.

Pfizer and Moderna's vaccines are extremely similar and both contain PEG.

The shots are messenger RNA-based (mRNA), and include a combination of fats, salts, sugar and acids, to carry the vaccine's critical genetic instruction manuals into the body, to teach it to fight off the coronavirus. Polyethylene glycol (PEG) is one of the fatty substances (or, lipids) included in both vaccines to help stabilize and package the key ingredients.

J&J's shot is different.

It works by injecting viral DNA into a person's arm, not mRNA. Instead of PEG, it has polysorbate in it.

But that doesn't mean J&J's vaccine is necessarily a better option for people with severe PEG allergies. The CDC stresses there is "cross-reactive hypersensitivity" between PEG and polysorbate, meaning that someone who's allergic to one substance could also react to the other.

"Polysorbate is a very similar chemical to polyethylene glycol," Jain said. "So, there is a good chance that if somebody is allergic to polyethylene glycol, they're going to be allergic to polysorbate as well."

People with PEG allergies may tolerate J&J's shot a little better

The US Food and Drug Administration (FDA) is not recommending that anyone with allergies avoid COVID-19 vaccination, categorically.

But, the CDC says that you should avoid any particular vaccine that contains an ingredient you are allergic to (such as PEG or polysorbate).

That's why Pat Wyman, CEO of HowtoLearn.com (a website focused on teaching people how to improve their learning and recall skills) waited until J&J's shot was available at her local pharmacy in order to get vaccinated.

Wyman is allergic to PEG, and even a little bit of it included in a face cream can give her a headache.

"I've had so many allergic reactions to medications," she told Insider, adding that she always carries around two EpiPens in her purse, just in case of an attack.

Her doctor recommended that she find a place offering J&J's single-dose vaccine, and Wyman did, at her local pharmacy, on March 10.

"We still have to exercise caution, but it makes me happier that I did it," she said of being vaccinated.

After vaccination, Wyman did have some severe vaccine side effects, including a high fever, chills, and a headache that began "two seconds" after vaccination she said, and lasted for five days. She thinks that's probably related to the vaccine's polysorbate component.

Still, as an immunocompromised person, she knows the risk of catching COVID-19 far overshadows that "temporary discomfort" of getting vaccinated.

"I would do it again in a heartbeat, because it is so important for me to feel safer in general," she said. "More than that, I want to be able to spend quality time with my family and be able to hug my children, and my grandchildren, and travel!"

Allergists are using laxatives to find out if patients have sensitivity to the COVID-19 vaccines

There are ways to find out if you might have an allergic reaction to a COVID-19 vaccine beforehand.

One good indication that you may be at risk, Jain said, is if you've already reacted to a previous vaccination (like the flu vaccine). If that's the case, consult an allergist before you get vaccinated.

If you are severely allergic to a particular vaccine's ingredients, your doctor may still be able to recommend a treatment that will make it safe to take the vaccine, though it is time-intensive.

"What a lot of allergists are doing now is systematically testing people for possible polyethylene glycol allergy," Jain said.

One way to do that in relative safety is for an allergist to administer their patient a bit of Miralax, a laxative that includes PEG. Then, the patient might start to feel nauseous or get a headache - red flags that they probably are sensitive to PEG.

After that screening, those people may choose to undergo desensitization. Jain's practice has desensitized several people to PEG after they had a reaction to their first dose of Pfizer or Moderna's vaccines.

The desensitization process involves two six-hour sessions, where patients are administered PEG in tiny, incremental doses, using an IV. Dr. Jain starts with a dose of .1 mg of PEG and increases the dosage every 20 minutes.

Patients must get their second dose of mRNA vaccine within 24 hours of their second IV session, as PEG stays in the body for a full day, and patients won't have a reaction during that time.

What to do before your vaccine appointment if you're nervous about having a reaction

Before going in for vaccination, people who are concerned about their potential for allergic reaction to COVID-19 vaccines may choose to take an antihistamine, like Zyrtec or Benadryl. Taking an antihistamine if you have mild symptoms after the shot is also fine, Jain said (though, if you're having any trouble breathing, seek clinical care).

Vaccination sites are also required to have epinephrine for allergic reactions on hand, but talk to your vaccinator to confirm that's the case, and let them know more about your specific allergy history. Then, make sure to stick around for a full 30 minute observation period after vaccination.

Take comfort when you leave the vaccine site then, knowing that almost all allergic reactions occur in the 15 minutes after vaccine administration.