Numbing Cream Safety: When Do Topical Anaesthetic Creams Used before a Procedure Become Dangerous?

What is a numbing cream, and before which procedures is it used?

The products popularly called numbing creams are known in medicine as topical (applied to the skin) local anaesthetics. They pass through the skin and temporarily stop the nerve endings from transmitting pain. The most commonly used active substances are lidocaine, prilocaine, tetracaine and benzocaine; some products contain two or three of these together. They come as creams, gels, ointments and sprays.

In medical aesthetics they may be used before procedures such as laser hair removal, laser tattoo removal, fractional laser, radiofrequency microneedling, microneedling, mesotherapy and fillers. They are not needed for every procedure; many people complete the procedure comfortably with cooling and similar methods. Your physician decides whether one will be used and which product is chosen.

When used with the product, amount, area and time set by the physician, these creams are generally considered safe, and serious toxicity is rare. Most of the problems are associated with the product being applied over a larger area than recommended, in an excessive amount, for a long time or under a covering.

How can a cream applied to the skin cause poisoning?

Local anaesthetics do not stay only where they are applied; some of the medicine passes through the skin and enters the bloodstream. When the amount reaching the blood is small, the body clears it without difficulty. When the amount increases, however, the medicine begins to affect the same conduction mechanism in nerve and heart cells, this time throughout the body. In medicine this is called local anaesthetic systemic toxicity; its most feared consequences are on the brain and the heart.

According to statements from the US Food and Drug Administration (FDA), the amount of medicine reaching the blood increases in the following situations:

• A large area: applying it to large surfaces such as the whole of the legs, the back or the chest.
• A thick layer and an excessive amount: using more than recommended, on the idea that 'the more I apply, the more it will numb'.
• A long time: leaving the cream on for longer than recommended, or reapplying it repeatedly.
• Covering: wrapping the treated area in cling film, a dressing or another covering.
• Damaged skin: applying it to skin that is irritated, has a rash, is broken, has shaving cuts or has recently been treated.
• Heat: a rise in skin temperature through exercise, a hot shower, a heating pad or tight wrapping.

The FDA also states that the amount of medicine passing through the skin can vary from person to person. For this reason, a way of using it that causes no problem in someone else may have a different outcome in you. The margin of safety is narrower for high-concentration products, for people with a low body weight and for children.

Why did the FDA issue warnings? The 2007 and 2024 warnings

In February 2007 the FDA issued a public health advisory about numbing products used before cosmetic procedures. The advisory refers to two women, aged 22 and 25, who applied numbing cream to their legs to reduce the pain of laser hair removal. Both women had wrapped their legs in cling film, as they had been told to, in order to increase the effect of the cream. Both had seizures, fell into a coma and died from the toxic effects of the medicine. The creams used had been prepared in a pharmacy and contained high amounts of lidocaine and tetracaine.

In the same advisory the FDA also stated that it had received reports of serious adverse effects after the use of these products in both children and adults, such as abnormal heart rhythm, seizures, coma and slowed or stopped breathing. The point the agency drew attention to was this: in medical procedures the cream is mostly applied by a trained healthcare professional; before cosmetic procedures, however, people may apply the cream at home, alone and unsupervised.

In March 2024 the FDA raised the subject again. This time the warning concerned certain over-the-counter (non-prescription) pain relief products marketed for use before, during or after procedures such as microdermabrasion, laser hair removal, tattooing and piercing. The agency reported that some of these products contained lidocaine at a higher concentration than is permitted for non-prescription products, and advised consumers:

• Not to use non-prescription pain relief products for application to the skin that contain more than 4% lidocaine.
• Not to apply these products heavily over large areas of skin or to skin that is irritated or broken.
• Not to cover the treated area with cling film or another covering.

According to the FDA, when these products are used in a way that increases absorption through the skin, they can lead to serious consequences such as abnormal heart rhythm, seizures and difficulty breathing; they can also interact with medicines and dietary supplements being taken.

The concentration limit given here is taken from a warning the FDA gave consumers about products sold without prescription in the USA; it is not a recommendation for use. In some procedures physicians may use products of higher concentration, limiting the area, amount and time, and under supervision. Which products are prescription-only or non-prescription may differ in other countries.

What is methaemoglobinaemia, and with which creams does it occur?

Methaemoglobinaemia is the conversion of the haemoglobin in the blood into a form that cannot carry enough oxygen to the tissues. Among local anaesthetics it is associated most with prilocaine and benzocaine. The FDA has reported that benzocaine can cause this condition and that it can be life-threatening; it has required a standard methaemoglobinaemia warning to be added to the information for all prescription local anaesthetics.

In a case series published by a poison control centre in France, three women who applied a cream combining lidocaine and prilocaine over a larger area than recommended before laser hair removal were reported to have developed methaemoglobinaemia together with cardiac and nervous system symptoms. The authors drew particular attention to the extent of the area treated.

Babies and young children, people with certain inherited enzyme deficiencies (for example glucose-6-phosphate dehydrogenase deficiency) and those taking medicines that can predispose to this condition are more susceptible. If this applies to you, be sure to tell your physician before the procedure.

What are the signs of numbing cream toxicity?

The signs can begin shortly after the cream is applied, and they can also appear after the cream has been wiped off. The early signs can be vague; for this reason they should not be taken lightly.

1. Remove the cream, and any cling film, immediately; gently wash the area with plenty of water and soap.
2. Call 112. If you are not alone, have the person with you make the call; try not to be left alone.
3. Lie on your back. Do not drive, and do not take a hot shower.
4. Tell the healthcare team the name of the product, its active substance, and how much you applied, to which area and when; keep the tube or box with you.
5. Even if the symptoms ease and pass, do not go ahead with the procedure without being assessed.

In Turkey, the National Poison Information Centre (Ulusal Zehir Danışma Merkezi, telephone 114) can also be consulted if poisoning is suspected; however, if you have the symptoms above, 112 comes first.

Can you be allergic to a numbing cream?

You can, but it is a different matter from toxicity. The most common form is redness, itching and raised skin developing over hours or days where the cream was applied (contact dermatitis). This kind of sensitisation is reported more often with ester-type substances such as benzocaine and tetracaine than with amide-type substances such as lidocaine and prilocaine. A serious allergic reaction with shortness of breath, widespread hives and swelling of the lips and tongue is very rare, but it is an emergency.

Temporary paleness or mild redness seen immediately after the cream is wiped off is most often due to the effect of the medicine on the blood vessels and does not mean an allergy. If you have had a problem with an anaesthetic medicine or cream before, say so before the procedure. We have explained the difference between allergy, fainting and other reactions in detail in our article “Allergic Reactions in Aesthetic Treatments”.

Can it be used in children, in pregnancy and while breastfeeding?

In these groups the decision rests with the physician alone. In children, body weight is low and the skin surface is relatively large; the same amount of cream can lead to a much higher blood level. Babies and young children are also more prone to methaemoglobinaemia. The FDA has stated that the serious adverse effects it reported also occurred in children. Do not adapt a cream, amount or time recommended for an adult to a child; keep the cream out of the reach of children.

In pregnancy and during breastfeeding, most cosmetic procedures can be postponed; if a procedure that requires a numbing cream is being considered, the benefit and risk are assessed together with the physician. You can find the general approach for this period in our article “Medical Aesthetics in Pregnancy and Breastfeeding”, and treatments under the age of 18 in our article “Medical Aesthetics for Young People”.

In people with a heart rhythm disorder or liver or kidney disease, and in those taking certain rhythm-controlling medicines, the clearance of the medicine from the body or its effect on the heart may also be altered. This is why it is important to tell your physician about all the medicines and supplements you take; we have put together what needs to be said to the physician before a procedure in our article “Preparing for a Medical Aesthetic Procedure”.

If I am going to apply the cream myself at home, what should I watch out for?

In some clinics the cream is applied in the clinic before the procedure; in others the patient is asked to apply it at home before coming. In the second case the instructions need to be written and clear. The principles below are consistent with the FDA's advice to consumers:

• Use only the product your physician has specified. Do not use products of unclear contents and concentration bought online, from a tattoo studio or from an acquaintance.
• Ask which area to apply it to, how much and for how long, and do not go beyond this. More cream, a longer time or a larger area does not mean 'more numbing'; it means more absorption.
• Do not wrap the area in cling film unless your physician has clearly told you to. If you have been asked to wrap it, ask separately for which area and for how long.
• Do not apply it to skin that is irritated, sunburnt, has a rash or has cuts; tell your physician about it.
• While the cream is on, do not exercise, take a hot shower or use a heating pad.
• If more than one area is to be treated on the same day, ask whether it is appropriate to apply the cream to all of them at once.
• Do not apply it around the eyes, inside the mouth or to the genital mucosa without a physician's advice; wash your hands after applying the cream.
• If you do not feel well after applying it, wipe the cream off and do not wait.

Numbed skin does not feel heat or pain. In energy-based procedures such as laser, this can make it harder to notice a burn early; if you feel unusual heat or burning during the procedure, be sure to say so. You can find pain and the options for relieving it in laser hair removal in our article “Laser Hair Removal”, and the tattoo removal procedure in our article “Laser Tattoo Removal”.

The person carrying out the procedure not being a physician, the cream being given to you without your being told its contents, or a verbal, general instruction such as 'apply it to the whole leg and wrap it in cling film' are signs that you should stop and think again. Our article “Counterfeit Products and Unlicensed Treatments” may guide you on this.