Novocaine Allergy Part I – The Esters

This will be the first of a three part series covering the various types of allergies associated with dental local anesthetics. Why write this? Well, some of the most frequently used search terms that cause people to arrive at this site are some combination of “allergy” and “novocaine.”

Needle used for novocaine injection at the dentist

People love to Google what they hate. And people hate the “novocaine” shot!

Over the years, I’ve observed that many of my own patients as well as readers and commenters on this blog think they may be allergic to the local anesthetic used at the dentist. This is not surprising given that over 1 million local anesthetic injections are administered each year in dental offices in the United States. With this level of frequency, adverse events are bound to happen, some of which may be interpreted as allergies.

The three parts are:

  1. The Esters
  2. Methylparaben and Sulfites
  3. True amide allergies

The titles of the three parts may appear cryptic, weird, or just plain boring. But this is how it needs to be organized. We’ll start with a brief history of local anesthetics.

Cocaine and Procaine

Coca leaves to make cocaine - a local anesthetic

If you crush these up you get dentistry’s first local anesthetic!

As I wrote about previously in the post Cocaine and Dentistry, cocaine was the first local anesthetic used in dentistry. Cocaine was first used in a dental procedure as an injectable local anesthetic in 1884. While it was a very effective anesthetic, there were unwanted side effects (euphoria, cardiovascular stimulation, addiction, etc.).

In 1905, another anesthetic was synthesized called procaine. It had all the anesthetic properties of cocaine but none of the undesirable side effects. Because of this, it was very quickly adopted, and a brand name version of procaine – novocaine – was launched.

What the Heck is an Ester?

Ester functional group seen in cocaine and novocaine

Chemical symbol of an ester (courtesy wikipedia)

An ester is a term from organic chemistry that describes a specific part of a molecule. I will not describe that portion in detail because it is so boring it will make 99.9% of you hit the back button on your browser!

The diagram here is not that important. What is important is that cocaine, procaine (brand name novocaine), and many other dental local anesthetics are considered “ester type anesthetics.” They are given this name for two reasons. First, there’s the obvious reason: they all contain an ester group. The second reason is to differentiate them from another family of local anesthetics called “amide type anesthetics.”

Allergies to Ester Based Anesthetics

Now we actually get to what everyone wants to know. And that is to begin talking about allergic reactions to dental local anesthetics. We begin with ester based local anesthetics because at one point these were the only local anesthetics available. I’ve organized the points in bullet format for easy reading:

  • When ester based local anesthetics are injected into the body, they are metabolized into a chemical called para-aminobenzoic acid (also called PABA).
  • PABA is known to cause allergic reactions in some people. So, back when novocaine was actually being commonly used (from 1905 to the mid 1950s), patients frequently experienced true novocaine allergies.
  • Because of the documented allergic reactions to PABA (caused by injections of ester based local anesthetics), ester based injectable dental local anesthetics are no longer used in the United States.
  • What is used instead? You guessed it – amide type anesthetics.
  • Ester based local anesthetics are only used in dentistry in the U.S. as topical anesthetics (also known as numbing jelly). The most common one is benzocaine.
topical benzocaine - an ester local anesthetic still used

Topical Benzocaine is still used in the U.S. routinely.

Other ester based local anesthetics besides procaine and benzocaine include tetracaine, chloroprocaine, propoxycaine, and cocaine. But note these are no longer used in dentistry in the United States.

So, to summarize, true novocaine allergies exist, but they do not occur anymore because novocaine is no longer used.

But what about allergies from other sources? What does a true allergy look like clinically? When my heart races at the dentist does that mean I’m having an allergic reaction?

These and other subjects will be covered in Parts 2 and 3…


  1. Two front teeth had fillings today. Upper lip now swollen? Why? I did NOT BITE my lip.

  2. Good info and blog, I like how clearly and easily you explain this information. Just as a minor addition to what you have here, many dentists don’t only use the traditional benzocaine 20% topical (similar to oragel), but are using stronger compounded topicals that work much better at numbing the soft tissues before the injection. Some of these formulations contain esters like Tetracaine.

    • Dustin,
      You are 100% correct. As an aside, benzocaine is an ester-style local anesthetic.
      Generally speaking, and I’m speaking very generally here, topical application of an ester-style topical anesthetic is going to be less likely to provoke systemic symptoms in an allergic individual than an injection. The injection contains a larger quantity of anesthetic and will enter the circulation much more rapidly than a topical one.
      I do use compounded topicals. My favorite is a mixture of tetracaine/lidocaine/prilocaine – where the tetracaine is an ester local anesthetic.

  3. Bob Miller says

    My mom told the Dentists and emergency room doctors, that I was allergic to Novocain beginning in 1966. I remember at least 3 times, they drilled on me with no local, then I was given Gas as an anesthesia, which I loved and would tell them it wasn’t doing anything and would be high as a kite for about 10 minutes after I was finished. When she told this complete fabrication to the ER doctor in 1967, I got 5 stitches to my upper lip with no local. In 1972 I needed 10 stitches in my head, and again I toughed it out. In 1974 I had an abscessed lanced and that hurt After that the dentists used lidocaine and I had stitches 2 more times with lidocaine.. In 2003, at 41 years old I got bit by a Hobo spider, I went to the ER and for some reason I answered that I was allergic to Novocain and the doctor said they were not going to use a local. I replied that I was not allergic to Lidocaine and he said if I was allergic to one “caine” I was allergic to all of them and tried to work on me with just a shot of morphine. I ended up being released without this thing being fixed and went to a surgeon the following day. I told him what was up, he had me sign a release of liability for the anesthesia, gave me 10 shots of lidocaine and cut the Necrosis from my leg. Why did they say allergy to one was allergy to all??? As it turns out, I never was allergic to anything. My mother has something wrong with her, I believe. She watched me scream my guts out as the doctor and his assistant held me down and lanced my ankle in 74, he even shoved a pair of scissors in the wound to break the deep puss pockets. Is there a connection between Novocain, Cocaine, and Lidocaine? Are they derived from Coca? Your thoughts.

  4. Rita Lloyd says

    I never had a problem with novocaine until I went through my change of life. I started to “rush” as I was told, so I received the shot without the epinepherine. That seemed better but I noticed a shakiness and weakness still afterwards. Now at the age of 66, I cannot take the novocaine, as just about 30 seconds after the injection, I feel as if someone has dosed me with arsenic or something lethal. I go ghost white, feel sicker that I ever have in my life, have extreme nausea and my heart flutters and I am so weak that I cannot speak. I actually fell like I am dying. It gets better after about 20 minutes but I am still weak and shakey to the point that I can’t drive myself home. I have to have someone take me to the dentist. I’ve been told not to have it again as I am having an severe reaction. I go home and stay on the couch the rest of the day as I am too weak to move and my heart is fluttering like crazy. An allergist told me she can’t test for novocaine alergies. Is this true? I’ve also had similar reaction to lidocaine and pontocaine. My dentist says that it is ridiculous, that no one is allergic to novocaine. I need help as I am having dental work and need some anesthetic.

    • Remember that novocaine is not used anymore. Allergies to the more modern local anesthetics (lidocaine, etc.) are VERY rare but still possible. Here in Connecticut, it is possible to be tested for allergies to lidocaine. I just had a patient tested 1 month ago (she was not allergic). So you can be tested by an allergist. I was not there for you reactions, but your description does not match the classic signs of an allergic reaction. My advice is to be tested for an allergy to lidocaine. If it is negative – which it likely is – then you and your dentist need to come up with an alternate hypothesis. My gut tells me it is vasovagal syncope (which I outlined here: but again I was not there so I can’t know for sure.

    • Could it be you have a latex allergy? There are rubber stoppers in medication bottles and cartridges. I’m thinking this may be why I had a recent reaction that laid me out for several hours after my dental appointment as well. I do have a latex allergy btw.

  5. Deb Fiske says

    I had a major reaction to benzocaine after using it a couple of times a day for two days. I suddenly had major swelling in my nose, mouth and throat and was taken to the ER by medics and diagnosed with an anaphylactic reaction to benzocaine. Needed epi, solumedrol, breathing treatments. MD said when I first arrived my Sats were in the 80s and she couldn’t see my uvula. I am new to town and am looking for a dentist. Is benzocaine related to any of the caines used in dentistry? I once had a pretty strong reaction to novocaine and I don’t think that is used anymore. I am now very afraid to go to the dentist. Thanks for any info you can provide.

    • Deb,
      Benzocaine is typically used in topical dental local anesthetics. It is an ester, which means that allergic reactions to it are somewhat common. It sounds like you did have an allergic reaction.

      Fortunately, INJECTABLE local anesthetics used in the U.S. are amide types. The incidence of allergies to amide types are extremely rare. You should be OK. But you should specifically tell the dentist to NOT USE ANY TOPICAL ANESTHETIC.

      If you are still having doubts, you can consult an allergist.