Allergy or Bad Reactions to Local Anaesthetics

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Written by the Dental Fear Central Web Team and reviewed by Lincoln Hirst BDS
Last updated on September 17, 2022

True allergies to the actual local anaesthetics used nowadays are extremely rare. Only a few cases have been reported worldwide. Some people are allergic to preservatives in local anaesthetics. But most of the time, people complain of symptoms like heart palpitations, shaking, sweating, or feeling faint.

On this page, you can find out about

True allergic reactions to local anaesthetics

I got a bad rash the last time I had local anaesthetic. My allergist has confirmed an allergy. What can I do now?

What is an allergy?

An allergy is a reaction the body has to a particular substance, to which it has become hypersensitive.

What are the symptoms of an allergic reaction to local anaesthetics?

Symptoms of an allergic reaction to local anaesthetics include

  • skin reactions (rashes, itching, oedema or hives)
  • asthma-like attacks
  • in the most extreme cases, anaphylactic shock.

Not all allergic reactions are dangerous. Most people who are allergic to local anaesthetics only experience temporary itching and skin rash after receiving the injection. Severe reactions are almost unheard of with local anaesthetics. You may find it comforting to know that dentists have to be prepared for medical emergencies, so they have the equipment and training to reverse such a situation.

What causes the allergy?

Local anaesthetic cartridges contain two active ingredients: the actual anaesthetic (which ends in -caine, e. g. lidocaine) and epinephrine. They also contain preservatives.

Most people who have a genuine allergic reaction to local anaesthetics are not allergic to the actual anaesthetic. It is much more common (though still rare) to be allergic to preservatives.

Why does local anaesthetic contain preservatives?

Epi quickly deteriorates and becomes useless if you don’t add preservative to keep it fresh. That’s why all standard local anaesthetics contain the preservative sodium bisulphite or metabisulfite.

Why use epinephrine in the first place?

Epi makes the local anaesthetic work more efficiently and last longer. It also acts as a vasoconstrictor: it stops soft tissues from bleeding.

Allergy to Preservatives

It’s possible to be allergic to some of the preservatives used in local, but the reaction is never severe, I’ve never heard of anyone having an anaphylactic response to them, but I suppose it’s possible. Usually, there’s a slight rash apparent for a day or two and that’s about it. – Gordon Laurie, BDS

If an allergy test shows that you’re allergic to the preservative, a local anaesthetic without epi can be used. As lidocaine doesn’t numb for very long without epi, a different local anaesthetic can be used. The options are prilocaine without epi (also known as Citanest Plain) or mepivacaine without epi (Scandonest Plain).

Bisulphites are preservatives used in both local anaesthetics and for keeping fruit look fresh

People who are allergic to bisulphites often know all about it, because they’re commonly sprayed onto fruit and vegetables to keep them looking fresh. If you have an allergy to bisulphites, let your dentist know about it!

Allergy to methylparaben

Methylparaben is no longer used in dental local anaesthetic cartridges. Allergy to methylparaben has increased over the years because of its use in drugs, cosmetics and foods. It may still be used in hospitals, but you’re safe at the dentist’s.

Allergy to Novocain

When talking about local anaesthetic, people from the U.S. often use the term “Novocain”… even though novocaine hasn’t been used in dentistry for decades. Novocain was an ester anaesthetic, as was the very first local anaesthetic: cocaine!

Allergies to esters are relatively common. Nowadays in dentistry, you’ll only find esters in topical numbing gels. Even there, their use has declined. Because they don’t enter the blood-stream, they can’t produce dangerous reactions.

Allergy to amide caines

Nowadays, all the -caines used for local anaesthesia are amides rather than esters.

Hardly anyone is allergic to amide caines:

In over 40 years as a dentist, I have encountered one person who had a genuine allergy to one of the local anaesthetics. Ironically enough, he was a dentist himself!

But there are a very small number of documented cases, so if you’re among them, what can you do?

There are a few possibilities:

  1. general anaesthesia in a hospital
  2. using a histamine blocker instead of an amide anaesthetic (stings and burns and is only suitable for emergency situations)
  3. going without local anaesthetic – a possibility for very minor work. For anything else, research shows that the work you have done will be much less successful and will fail sooner
  4. in some cases, hypnosis can work for pain control
  5. using a different -caine local anaesthetic (the best option)

1. and 2. should only be used in acute emergencies, if there really is no time for an allergy test. Otherwise, an allergy test will show which of the -caines are safe for you.

Local anaesthetic choices

The 5 local anaesthetics used in dentistry today (in order of popularity) are:

  • Lidocaine Hydrochloride (UK: Lignocaine) (tradenames: Xylocaine, Alphacaine, Lignospan, Octocaine)
  • Articaine Hydrochloride (tradenames: Septocaine, Septanest, Astracaine, Ultracaine)
  • Prilocaine Hydrochloride (tradename: Citanest)
  • Mepivacaine Hydrochloride (tradenames: Carbocaine, Arestocaine, Isocaine, Polocaine, Scandonest)
  • Bupivacaine Hydrochloride (tradename: Marcaine)

Luckily, there is no cross-allergenicity with amide local anaesthetics – meaning that someone may be allergic to lidocaine and mepivacaine, but not to articaine, for example.

Tips for dealing with a suspected true allergic reaction

  • An allergist can test which substance exactly you are allergic to. Your dentist should request testing two or three different amide local anaesthetics as well as sodium metabisulphite.
  • They should test local anaesthetics (caines) without the epinephrine, and test preservatives separately.
  • If it turns out that you really are allergic to a caine, an allergist can help you find out which of the caines you can tolerate.
  • If it turns out that you are allergic to sodium bisulphite, your dentist can use a local anaesthetic without epi: either mepivacaine without epi (Tradename: Scandonest 3% Plain) or prilocaine without epi (Tradename: Citanest Plain).

Other adverse reactions (heart palpitations, shaking etc.)

My last experience with getting numb was horrible. I felt flushed, dizzy, rapid heartbeat, full panic attack and almost fainted within 3 minutes of getting injected. Now I’m terrified of it happening again!

Is a racing heart and shaking a sign of allergy to epinephrine?

It is physically impossible to be truly allergic to epinephrine. Here’s why: epinephrine, or epi for short, is the same as adrenaline. Our bodies produce adrenaline all the time.

Symptoms like:

  • a racing heart
  • shaking uncontrollably
  • breaking out in a cold sweat
  • not being able to breathe properly or breathing rapidly
  • feeling dizzy or lightheaded
  • tingling in the fingers, toes or lips
  • a headache afterwards

are all signs of an adrenaline rush.

What can cause such a reaction?

1. Injecting into a blood vessel

A reaction to epi is a normal response when it’s been injected into a blood vessel (either a vein or an artery):

Most of the time when we get a response like this it’s because a little bit of the LA solution was accidentally injected into a vein. This is harmless in itself for most people, but it also usually goes with a sort of panic feeling as well as a feeling of “heart pounding”. Also fairly harmless but quite scary! It can be mostly avoided by careful technique by the dentist but very occasionally, accidents will happen. – Gordon Laurie, BDS

The resulting adrenaline concentration in the blood is unlikely to be any greater than that produced by the body under stressful situations or during exercise. And it is no more dangerous for most people 1. Your body will happily metabolise both the LA solution and the epinephrine.

An exception is if somebody already has undiagnosed and untreated very high blood pressure. In this case, in theory, it could provoke a more serious reaction. So do let your dentist know about existing health conditions or concerns.

An accidental injection into a blood vessel is unlikely to happen to you ever again. Do let your dentist know about your bad experience though so they can make extra sure!

2. Anxiety

Anxiety is a common cause of an adrenaline rush. The amount of epi in local anaesthetics is small compared to the amount your body naturally pumps out. Anxiety makes your body produce adrenaline to prepare you for a fight-or-flight situation – an increase in heart rate and blood pressure means that you can run away faster!

N.B. If you do decide to do a runner, please let your dentist know first – that way, they’ll be able to remove any sharp objects between you and the door.

3. Sensitivity to epinephrine

We can’t rule out the possibility that some people really do react more sensitively to the injection of epi than others. If the epi is a major concern to you, simply using an epi-free alternative is often the easiest solution.

Epinephrine and medical conditions

Let your dentist know if you have any medical conditions, and also tell them what medications or drugs you’re on, especially:

  • high blood pressure
  • a previous heart attack
  • bypass surgery
  • angina
  • uncontrolled diabetes
  • an uncontrolled thyroid disorder
  • or if you’re taking beta-blockers, tricyclic antidepressants or cocaine.

With some of these conditions, a dentist may prefer to use an epi-free local for injections in certain parts of the mouth.

Not having adrenaline in local due to heart issues is not really necessary, it’s rather an old-fashioned point of view. However, there are plenty of good alternatives so some dentists go along with the patient on it rather than have an argument about it. – Gordon Laurie, BDS

Alternatives to epinephrine

You can limit the amount of epinephrine by

  • choosing a plain local anaesthetic solution (without epi)
  • choosing a solution with minimal epi concentration
  • using an injection technique which requires a smaller amount of local anaesthetic.

1. Local anaesthetics without epinephrine

It is certainly the case that local anaesthetic with adrenaline or epinephrine will keep you numb for longer. This is because the epinephrine is a vasoconstrictor, meaning it cause the local blood vessels to constrict, thus keeping the local anaesthetic in the area by slowing the rate at which is is washed away by the blood.

But for most dental treatments, the local anaesthetics without epi are just as effective as those with.

If there’s no epi in the solution, then it’s pretty much impossible that you’ll get the same symptoms as the last time. And if you do, you’ll at least know that the symptoms are due to anxiety rather than the epi.

What are the alternatives?

There are two local anaesthetics which work for a reasonable amount of time even without epi:

  • mepivacaine without epinephrine (Tradename: Scandonest 3% Plain) and
  • prilocaine without epinephrine (Tradename: Citanest Plain).

There are also local anaesthetics which contain an epinephrine-free alternative such as Felypressin.

A girl using inhalation sedation

The choice will depend on the actual tooth or teeth being worked on and how long the procedure takes. For example, Citanest Plain lasts for 1 to 1.5 hours for lower teeth (when using an inferior alveolar nerve block). However, for upper teeth, it lasts much shorter than standard local anaesthetic.

So what can you do for longer procedures?

There is no reason why you cannot use epi-free alternatives for longer procedures like root canal treatment. They can still get the tooth very numb to start with. As far as duration of action goes, the critical phase of a root canal is the initial bit where you remove the dying nerve. This is when you need the tooth to be properly numb. Once this is done, there is very little sensation left in the tooth. So if the local started to wear off later on, you would probably not even notice it. If you did, another top-up injection could be given. – Lincoln Hirst, BDS

Sometimes, it may be more difficult to get totally numb without epi. In this case, using nitrous oxide or IV sedation in addition to the local anaesthetic may be helpful.

2. Limiting the amount of local anaesthetic

Another option is finding a dentist who uses a computer-controlled local anaesthesia delivery system like The Wand STA. Some injection techniques that are possible with the Wand use far less local anaesthetic than traditional techniques.

3. Doing the treatment without local

This is not a great idea. Apart from being painful, treatments statistically are less successful when done without numbing. So it’s likely to need to be redone more quickly.

Tips for coping if you are concerned about epinephrine

Most commonly, what feels like an allergy to local anaesthetic is really an adrenaline rush. Here are a few tips for coping:

  • If you feel anxious about injections or upcoming treatment, talk to your dentist about it. Most dentists will be extra gentle with you if they know about your fears and do their best to calm and reassure you.
  • Perhaps just understanding what is happening and knowing that an adrenaline rush is not dangerous, but a natural reaction, might make injections easier for you. The sensation is unpleasant, but not dangerous.
  • Your dentist may be able to offer you laughing gas, IV sedation, or anti-anxiety medications.
  • Distraction techniques such as listening to music can help.
  • Some dentists tell their patients beforehand that the injection contains adrenaline and that they will feel an increase in heart rate, which is not dangerous. Some people find this helpful because it prepares them for the possibility that they’ll feel their heart beat faster. Better still, one can attribute any adrenaline rush to the drug, rather than to anxiety. Unfortunately, this technique can also backfire and make people panic instead!

Local Anaesthetic Overdose

This is probably not an issue unless you’re having a lot of treatment in one go. Even then, it is almost never dangerous in adults. For example, one study cited by local anaesthesia guru Stanley Malamed showed one particularly LA-happy general dentist using an average of 19.24 cartridges of local anaesthetic (per person!) for the removal of all 4 wisdom teeth2. Gulp. Clearly, a lot of these patients received an overdose, yet none of them experienced any adverse reactions. This kind of shows that local anaesthetics are extremely safe for healthy adults.

Some people are concerned because they’ve read about deaths following local anaesthetic overdose (invariably in the US) on the Internet. What usually isn’t reported is that the few serious incidents which have occurred involved very bizarre circumstances:

Heard of a case in the USA where the “dentist” (and I use the word very loosely) injected 20 carts to a patient who was having problems during an IV, because he wanted to get some adrenaline in!!! Patient died, dentist convicted of manslaughter.

But what if the local anaesthetic was injected straight into an artery or a vein? Is there a chance of dying from lidocaine toxicity or similar?

Assuming you’re a normal adult, the dentist would need to repeat that feat around forty times. It simply is not possible to inject enough local anaesthetic solution into a vein. The veins in the area where the injection goes are so small and delicate that they would be utterly destroyed within the first 2 or 3 attempts. Remember too, the murderous dentist would be aiming for a structure about 1 mm in diameter which is 3 cm buried inside the tissues and completely invisible. Injecting into an artery with a dental needle is simply impossible, the arterial wall is far too thick and the fine dental needle won’t penetrate it. – Gordon Laurie, BDS

Tips for coping if you are concerned about an overdose

  • An overdose is only ever a potential concern when you are having a lot of dental work done in one go, especially when it’s in all 4 quarters of your mouth (upper and lower left and right).
  • Let your dentist know about your concern and discuss the options. For example, if there is a pressing reason to numb all 4 quarters during the same appointment, your dentist can administer local anaesthetic to one quadrant, treat that area, then numb the next quadrant, and so on. This means a lower concentration of local in the blood compared with giving the local all at the same time.

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Sources of Information

  1. UK Medicines Information. What is the clinical significance of potential drug interactions with local anaesthetic preparations used in primary care dentistry? Published 30 July 2020.[]
  2. Stanley Malamed (2004). Handbook of Local Anesthesia, Fifth Edition, p. 313. St. Louis, Missouri: Elsevier Mosby.[]