Novocaine Allergy Part II – Methylparaben and Sulfites

In Part I of this series, I covered allergic reactions to ester based local anesthetics used in dentistry. These occur very rarely now because the entire class of ester local anesthetics have essentially been phased out in favor of amide based local anesthetics. Nevertheless, allergic reactions can and do occur after the “novocaine shot.” So the question is, what is/are producing the reactions?


chemical structure of methylparaben


Methylparaben is a preservative used in the pharmaceutical, personal care, and food industry. It is found in many cosmetics currently on the market in both the United States and elsewhere. Methylparaben was at one point included as a preservative in dental local anesthetics. Its main function was to inhibit the growth of bacteria and to help maintain the sterility of the anesthetic.

Methylparaben is chemically very similar to PABA – the metabolic by-product of many ester-type local anesthetics. As I outlined in Part I of this series, PABA can produce allergic reactions in some individuals. Because of this similarity to PABA, when methylparaben is injected as part of a local anesthetic, allergic reactions can occasionally occur.

Because of this, since the mid 1980s, the U.S. Food and Drug Administration mandated the removal of methylparaben from single use dental local anesthetic cartridges. As a result, unless the dentist is using local anesthetic from a multi-use container (which is incredibly unlikely in your typical private practice in the U.S.), you will not be exposed to methylparaben as part of the local anesthetic injection.

Some multi-use vials of local anesthetic still contain methylparaben. But those are typically seen in hospital settings and in individual physician offices.

Since I have never used a dental local anesthetic with methylparaben in it, I have never seen an allergic reaction firsthand.

Sulfite Sensitivity

Sodium metabisulfite used as a preservative in dental local anesthetics

The label from a box of lidocaine with epinephrine used in my office in Connecticut. Metabisulfite is a component.

Sulfites are a class of chemicals used a preservatives. Like methylparaben, sulfites are used in a variety of ways. They are most commonly used to preserve food and can frequently be found in wine, jams, some frozen seafood, and many other products.

In dentistry, sulfites are added to local anesthetics that contain epinephrine. The sulfite – most commonly seen as potassium metabisulfite – is used to prevent the breakdown of the epinephrine. This allows the local anesthetic to have a shelf life of more than a year.

Exposure to sulfites in food as well as a “novocaine shot” can provoke allergy-type symptoms in susceptible individuals. If you have asthma, you are much more likely to be sensitive to sulfites than non asthmatics.

So what would an allergy to sulfites look like? I personally have never seen one. In this article, a patient was injected repeatedly on one side with a dental local anesthetic containing metabisulfite. Within a day, she was experiencing mild swelling at the injection site. After a couple of days, she experienced severe facial swelling with pain and was admitted to the hospital. Allergy testing later concluded an allergy to bisulfite found in the local anesthetic.

Bupivacaine with epinephrine using metabisulfite as a preservative

Box of bupivacaine showing sodium metabisulfite as a component.

So, if you suspect you may have sulfite sensitivity, be sure to ask your dentist to use a local anesthetic that does not contain epinephrine. Dental local anesthetics that do not contain epinephrine do not have metabisulfite.

There is an important distinction between sensitivity to sulfites and allergic reactions to sulfites. The Cleveland Clinic has a nice summary located here.

Note that sulfite sensitivity and sulfa-drug allergies are totally different! So if you have an allergy to sulfa drugs – more formally known as sulfonamides and includes the brand name Bactrim – it does not mean you are allergic or sensitive to sulfites. And vice versa. The reference is located here.

So what’s next in Part III? We’ll cover true allergies to dental local anesthetics – which are extremely rare but have been found.


  1. Thank you for this information. I also had a frightening experience on dental chair. Epinephrine was used. After 1-2 seconds I felt like my heart would jump out of my chest. In about 12 hrs I had to visit an urgent care and was told to go to hospital emergency. My symptoms: tachycardia. My heart rate was fast even when resting in bed. Blood pressure at one point was 180 and heart rate 115bpm lying down resting. Not allergic to lidocaine when tested later. Metoprolol was prescribed. That helped control my tachycardia and lower bloood pressure. Every visit to dental thereafter, I asked for a plain medicine: no epi
    Still not sure if I really have sensitivity or allergic to epinephrine. I am scared to even go thru- testing. I was traumatized by the experience that I get scared to even find out thru skin testing if I really have sensitivity or allergic to epi. What is your opinion about my case? Btw, my lidocaine testing was at my allergist clinic.
    Thank you

  2. LAURIE D HAZEN says

    As am asthmatic I have a severe sensitivity to sulfites so I can tell you what a reaction would be like. . My first major episode occurred when I was eating dried fruits which I later found out are loaded with sulfites to keep them from browning. Within a few minutes I could feel my throat swelling and I couldn’t breathe, and ended up in the ER. I now eat only fresh meats and veggies so I haven’t had an episode in a while. I haven’t been to the dentist in years because I’m deathly afraid of whatever they’ll use to numb my tooth but I need to go. I just hope the dentist I choose is knowledgeable about sulfites..

    • Laurie,
      It is great that you are knowledgeable about your condition. Regrettably, most dentists are not aware of the presence of sulfite preservatives in many local anesthetics. However, nearly all dentists will be receptive if you mention this to him/her in advance of the procedure. Just make sure you say something along the lines of “I have severe sensitivity to sulfites, including the sulfite preservative used in epinephrine containing local anesthetics. Can you use a local w/out epinephrine?” Just don’t say something claiming you’re allergic to epinephrine. That is not accurate and even more so physiologically impossible.

      • I am very allergic to sulfites and had no idea it was used in dental medication so did not mention it and had a horrible experience. I will mention the allergy to sufites next time, but could you give me some ideas of alternative local anesthetics a dentist could use?

        • Local anesthetics that contain epinephrine need the sulfite preservative. Local anesthetics that do not contain epinephrine do not include sulfites. If you mention this to your dentist, and he/she uses local w/out epinephrine, that should eliminate the sulfite issue.

          • Thank you! The dentist asked me if I was allergic to anything and I said,”No.” I thought sulfites were only in food! It was only in research that I found out it is in some medications also. I will be sure to mention it to any dentist as well as any physician in the future. Thanks for the help!

  3. Mary Malseed says

    I’ve read all your information online because I am in bed with yet another botched job 3 days ago of a dentist mistakenly giving me local anaesthetic with epinephrine instead of without. I reminded my dentist seconds before, but she says her nurse made a mistake handing her the wrong injection! Evidently she didn’t check it herself.
    Symptoms the same as many already mentioned, attended emergency at hospital, and each time this happens to me it’s a little more severe and taking longer to get over the residual effects.
    Years ago I thought it was an allergic reaction, but now call it a severe adverse reaction. I assumed it was to epinephrine, but now think it’s probably two-fold: allergy to sulphites, the preservatives used, plus me having an increased amount of adrenaline receptors. I have had asthma, eczema and hives earlier in my life, am a health nut and so now have no exposure to preservatives in my everyday life.
    Incidentally, at least one of my sons has the same reaction (don’t know about the other, I’ve never allowed him to have adrenaline), as does my sister and her daughter.
    I think it’s semantics or splitting hairs to argue about the terms “allergy” versus “adverse reaction” for the patient. I understand full well your insistence on the technical difference, but that seems to me to be deflecting attention away from the real problem – dentists using epinephrine when mostly they don’t have to.
    I am determined never to be in this situation again, where I can’t go to work or even do basic housework chores until this wears off. My children and I from now on must all personally do a visual check on the injection formulation before it goes into our mouths, same as we have to verify our name and date of birth on a blood vial in the pathology clinic.
    Mary M

    • Mary,

      I’ll make 2 comments. First, I am glad that you are acknowledging that you experienced an adverse reaction (as opposed to an allergic reaction). That was the point of this post.

      I bolded your commend when you asserted that, for most of the time, dentists do not have use epinephrine. I disagree. I’ll give you an example. Just last week, I had to do 2 fillings on a pregnant patient whose OB had requested no epinephrine. I’ve done fillings on her before using local with epinephrine with no issue when she was not pregnant. For each tooth, I literally had to inject her six or seven times. And in the end, she still felt some discomfort during the procedure.

      If you wish to have local without epinephrine, that is your choice. But don’t generalize and start asserting that it’s not needed. Because that is not correct and there is ample research supporting the need for epi in local anesthetics to enhance local anesthesia.