Impact of Laser Refraction and Ambient Light on Sensor-Based Automatic Hand Sanitizer Dispensers

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Cosmetic lasers are commonly used in dermatology in several settings, including academic dermatology. In many academic dermatology settings, the rooms where laser treatments are conducted have sensor-based automatic hand sanitizer and soap dispensers in place. While these sensor-based devices facilitate quicker sanitization for physicians between routine patient interactions, as opposed to traditional handwashing, their malfunction can be disruptive to the establishment of rapport during the consultation.

In our academic dermatology clinic, the automatic hand sanitizer dispensers in the laser rooms were noted to dispense at seemingly random occurrences, consequently interrupting patient interactions and resulting in waste of resources. On further investigation, the timing of the dispenses was noted to occur during the performance of the neodymium yttrium aluminum garnet (Nd:YAG) laser on settings for hair removal and scar remodeling. The problem persisted after performing routine troubleshooting maneuvers, such as cleaning the sensors, changing the batteries, restarting the sanitizer and soap units, and ensuring that all glass in the room was covered. The only solution was to temporarily disassemble the machines before using the Nd:YAG laser.

Most automatic hand sanitizer dispensers detect hand motion by using electromagnetic energy to emit infrared rays ranging from 700 nm to 1 mm in wavelength.¹ The consistent electromagnetic contact of the indwelling light-emitting diode (LED), usually found at the top of the device, with a light dependent resistor (LDR), usually located at the base of the device, acts as a sensing element. When the hand obstructs this communication, the raysfrom the LED are blocked, the resistance of the LDR increases, and the circuit relay causes the dispensing of a predetermined amount of hand sanitizer.² These sensor-based automatic hand sanitizer dispensers additionally sense changes in ultraviolet and ambient light intensity, therefore making them susceptible to environmental changes.

The main factor that we postulated contributing to the circuit disruption in our sensor-based devices is the refraction of light. If cryogen spray is used for cooling and moisture is present in the air, small ice crystals will form on the sprayed surface, which can reflect a substantial part of the laser light.³ However, instead of cryogen spray, the Nd:YAG laser in our clinics uses a built-in copper cooling device or air cooling method. These cooling methods theoretically have no medium disturbing the path of the laser beam and no interface that would result in energy losses caused by dispersion, transmission, or reflection.

Gel is routinely applied to the skin for additional cooling, as well as to facilitate smooth gliding when the handheld portion of the laser is in contact with the skin. The gel could theoretically increase the risk of refraction, causing beams from the laser to interfere with the circuit relays of the dispensers. However, the authors have found that the automatic dispensers are triggered both with and without the use of gel. Further, the proximity of the laser device and direction of the laser (shone toward or away from the automatic dispenser) do not appear to influence the frequency of erratic dispensing. Therefore, an additional hypothesis for the observed phenomenon is interference from the electromagnetic radiation within the circuitry of the laser.

In conclusion, automatic hand sanitizer dispensers have become increasingly popular due to the ease of compliance; however, they may not be the first choice for sanitization in laser rooms if laser devices cause unwanted dispensing. Manufacturers and practitioners may benefit from being advised of this potential interaction.

Disclosure: Dr McMichael has received research grants, royalties, and/ or consulting support from a variety of companies, including Allergan; Almirall; Arcutis; Bioniz; Cassiopea; Concert Pharmaceuticals; Covance; eResearch Technology, Inc; Galderma; Incyte; Informa Healthcare; Johnson & Johnson; KeraNetics; Lilly; Merck & Co, Inc; Pfizer; Proctor & Gamble; Revian; Samumed; and UpToDate. Dr Palmer reports no relevant financial relationships.

References

1. Mujawar M. Design of compact and cost-effective automatic sanitizer dispenser machine. Int Multidiscip Res J. 2020;2(4):13-17.
2. Suryawanshi VR, Surani HC, Yadav HR. Sensor-based automatic hand sanitizer dispenser. Med J Dr DY Patil Univ. 2021;14(5):543-546. doi:10.4103/mjdrdypu. mjdrdypu_221_20
3. Grad L, Sult T, Sult R. Scientific evaluation of VSP Nd: YAG lasers for hair removal. LA&HA. 2007;2(2):1-11.