Dental MythBuster #14: A Swollen Lip After a Dental Visit Means You’re Allergic to Novocaine

This is one dental myth that every dentist has to deal with at some point. And that is the myth that if a child’s lip swells up after a dental visit where local anesthetic was used, it always means the child must be allergic to something the dentist injected.

And to make matters worse, this myth is then often propagated by the child’s pediatrician.

What would you think if you saw this the day after your 8 year old got a filling on his lower right molar:

swollen lip from biting while numb after filliing

Lower right lip swollen after a filling was done on the lower right.

That looks pretty nasty right? Something clearly happened here. In my own experience, and in talking to other dentists, parents generally do one of four things upon seeing this:

  1. Parent immediately heads to the closest ER or emergency walk-in clinic.
  2. Parent immediately calls the pediatrician for an emergency appointment and is seen that day.
  3. Parent gets on Google, becomes almost immediately convinced of an incredibly dire situation, and then does either #1 or #2.
  4. Parent calls the dentist office.

Wouldn’t it make sense to call the dentist office? After all, it was the dentist who did the procedure, wouldn’t he/she know what is going on?

But unfortunately, options 1, 2, and 3 are often pursued. And in many of those cases, an incorrect diagnosis is frequently made, which leads to unnecessary finger pointing, as well as wasted time, confusion, and missed school for the child.

So, what does it mean when the lip swells up after a dental appointment when local anesthetic was used?

Swollen Lip = Lip Biting While Numb (99.99% of the time)

Here are two cases I’ve seen in my office:

swollen lip after dental work means lip biting

Swollen lips after dental work. Both patients admitted that they inadvertently bit and/or played with their lips while numb.

The above photos look unpleasant, right? In both cases, lower teeth were given local anesthesia, and that numbness extended to the lip. And in both examples, the patients admitted to repeatedly biting their lip.

The repeated biting led to swelling, bleeding, and bruising. Many times, the child has no recollection of doing it, because the child was numb and felt no pain. But the next day – whoa!

It is quite easy to see how this can come from biting. Go ahead and try to bit your lower right lip with your upper front teeth. Easy, right? Do this a couple of times very hard while you’re numb and you’ll end up looking like the one of the photos.

Why This is not an Allergy

Despite seeing this on a regular basis, many dentists (myself included) still have to deal with accusations and/or false diagnoses of allergies from the injection. Here are some key points:

  • Location. The injection site is nearly always located far away from the traumatized area – in some cases nearly two inches. If it were an allergy, why then is the injection site totally normal? See the photo below.
  • Appearance. In general, allergic reactions do not produce a localized ulcerated area away from the injection of the alleged allergen. The appearance of this is simply not consistent with an allergic reaction.
  • Lack of Systemic Symptoms. Even less severe allergic reactions will produce other symptoms such as dry mouth, hives, and other findings. None of these are typically present in lip biting.
dental injection photo next to tooth

Dental injection adjacent to a 12 year molar. How could this produce an “allergic” reaction on the lip only when the injection site is so far away?

Of course, allergic reactions can occur from the injection. However, they are exceedingly rare, and don’t present like this. For more information, see this three part series.

What Should You Do?

So, if you or your child’s lip is swollen after receiving local anesthetic, what should you do? Call your dentist. Generally speaking, pediatricians, PAs, and NPs do not have experience seeing these types of things, and then come up with what we call “creative diagnoses” which are usually incorrect. General dentists and pediatric dentists see lip biting all the time and can guide you on how to handle it.

But to stress this point, it is a myth that a swollen lip (in the absence of other findings) after a dental visit means you are allergic to lidocaine (mistakenly called novocaine).

Until the next dental myth is busted…


  1. dentistdelraybeach says:

    Oh I’m so glad you posted this. I am sure they will really helpful! Thanks for sharing these tips!

  2. What about if the tongue, throat, and face swells as well?

  3. What if your top lip starts turning white on the outside? It’s like the lip is turning white….

    • It is very rare for the upper lip to be bitten while numb but still possible. Regarding the white color, there are many more details needed to figure out what might be going on.

      • My son (6) had a top back tooth pulled today and now his top lip is swollen. I did catch him biting and sucking on it some but stopped him as soon as I saw him doing it and the swelling hasnt went down at all . Do I need to give him some Benedryl? We have done ice pack on it all afternoon and Motrin. He’s asleep now so I pray he will wakes up and it’s down.


  4. 3 shots of lidocaine when I got home in the evening my lower left side of my lip starting swelling up. This never happen to me. Maybe to much lidocaine ?

  5. Patricia Gaffney says:

    I had a filling done yesterday on the lower left molar and was given an anesthetic by injection. Today later that day after the anesthetic worn off I developed a prominent swollen lower left lip, which I still have today. My question is, if this is the effect of an allergy why is it I have never had this reaction before. I have had many such injections over the years. What other reason could there be for this swelling if not a reaction to the anesthetic?

  6. Am so glad this is on here,my 10yr old had filing Thursday morning an those pics are exactly the same as my daughters but alot bigger.yes she bit her lip not knowing due to numbing.
    So what do I do next?

    • Jo,
      You’ve probably already resolved the issue. But the first step is to call your dentist. Treatment is usually palliative – ice/cold to reduce swelling, children’s motrin, etc. But always defer to your dentist.

  7. Ella Dornseif says:

    If you bite your top lip a lot will it also turn out like that?

  8. Thank you for clearing that up. My lower lip is a mess today after anaesthetic yesterday. I’m guessing I must have bitten it while eating when still numb.

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