Dermatologists routinely employ numbing agents to prevent pain during minor surgical procedures, skin biopsies, and certain cosmetic treatments like laser resurfacing or filler injections. These agents safely and effectively block pain signals from the procedure site to the brain. This localized approach allows patients to remain fully conscious and comfortable. The choice of numbing method depends heavily on the depth and extent of the procedure being performed.
Topical Anesthetics for Surface Procedures
For procedures that only affect the skin’s surface, dermatologists often apply topical anesthetics, which are creams, gels, or patches applied directly to the skin. These agents work by penetrating the outermost layer of the skin and temporarily blocking the sodium channels on the sensory nerve endings located in the superficial dermis. By inhibiting the influx of sodium ions, the nerve cannot initiate or transmit the pain signal. One common formulation is a eutectic mixture of local anesthetics, which combines 2.5% lidocaine and 2.5% prilocaine in a cream base (EMLA). High-concentration lidocaine creams (up to 5%) are also frequently used for procedures like superficial laser treatments or microneedling. For these topical agents to be effective, they require sufficient time to absorb, often needing an occlusive dressing and a waiting period of 30 to 60 minutes. The primary limitation is that topical numbing only provides analgesia to a shallow depth, typically a few millimeters, making it unsuitable for deeper surgical excisions.
Injectable Anesthetics for Deeper Procedures
When a procedure requires work below the surface of the skin, such as a deep shave biopsy or the removal of a larger skin lesion, injectable local anesthetics become the primary method. This technique, known as infiltration anesthesia, involves injecting the agent directly into the tissue surrounding the area to be treated. Lidocaine is the most widely used injectable anesthetic in dermatology due to its rapid onset and favorable balance between potency and toxicity.
Lidocaine is often combined with a vasoconstrictor, such as epinephrine, to improve the anesthetic effect. Epinephrine causes the surrounding blood vessels to narrow, which slows the rate at which the body absorbs the lidocaine, thereby prolonging the duration of the numbness and reducing bleeding at the surgical site. Historically, this combination was avoided in areas like the fingers, toes, and nose due to concerns about blood flow restriction, but recent consensus shows that using lower concentrations is safe and effective in these areas.
A significant patient comfort measure is buffering the anesthetic solution with sodium bicarbonate. Standard lidocaine with epinephrine is slightly acidic, which causes the sharp stinging sensation when injected. Adding alkaline sodium bicarbonate raises the solution’s pH closer to the body’s natural pH, substantially reducing the initial sting and speeding up the onset of numbing. Buffering the solution can reduce injection pain by 20% to 40% compared to using unbuffered lidocaine.
Physical and Adjunctive Numbing Techniques
Dermatologists employ non-pharmacological methods alongside chemical agents to enhance patient comfort, especially during the initial moment of injection. One simple and immediate method is localized cooling, using ice packs, cold air, or a cryo-spray applied just before the needle enters the skin. This temporary cooling provides a brief numbing effect on the surface, which distracts the sensory nerves from the pain of the needle stick.
Another adjunctive technique is the application of vibration near the injection site. Devices that produce a high-frequency vibration are placed on the skin a few centimeters away from where the needle will be inserted. This works based on the Gate Control Theory of Pain, which proposes that non-painful stimuli, like vibration, can travel along the same nerve pathways and effectively override the pain signal before it reaches the brain. While vibration does not eliminate pain entirely, it makes the procedure much more tolerable for patients, particularly those who are needle-phobic.
The Patient Experience Onset and Duration
The patient experience varies depending on the method of anesthesia used. When a local anesthetic is injected, the numbness is often immediate, beginning within a few minutes. Patients typically feel a brief, sharp sting from the needle and the acidic solution, followed quickly by a complete loss of sensation in the treated area. Injectable lidocaine provides effective pain relief for one to two hours, but when combined with epinephrine, the duration of numbness can be extended up to four hours, as the epinephrine slows down the clearance of the drug.
In contrast, topical anesthetics have a much slower onset, requiring a waiting period of 30 to 60 minutes under occlusion to achieve adequate numbing depth. Once numbing is achieved, the effect is shorter-lived than with an injection, often lasting only 60 to 90 minutes after the cream is removed. Patients should be cautious about resuming activities that require fine motor control if the procedure involved the hands or feet, until full feeling has returned.