Aesthetic Laser Physics, Terminology, and Skin-Tissue Interactions

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Have you ever wanted to know more about aesthetic lasers, but don't know where to start?  Confused by the lingo? Join Dr. Nicole Langelier as she takes Dr. Christina Choe and Dr. Sandy Zhang-Nunes through a whirlwind tour of laser physics, laser terminology, and laser-tissue interactions. We'll explain how lasers work, discuss selective photothermolysis, cover basic skin anatomy, and define workhorse terms like chromophore, wavelength, joules, watts, fluence, thermal relaxation time, and pulse width. Consider this the prequel to upcoming episodes on the clinical uses of ablative laser resurfacing, non-ablative laser resurfacing, light and energy based devices.  By understanding the language and core scientific concepts of lasers, we hope to make you a safer and more educated laser provider!

 

Corrections/Clarifications:

- Blood vessels are lined by endothelium (not epithelium)

- The skin registers pain from heat at 45C, but may occur between 43-44C with variability based on the time of exposure and area of exposure (I stated it occurs at 42C) https://www.cardinalhealth.com/content/dam/corp/web/documents/whitepaper/cardinal-health-localized-temperature-therapy%20White%20Paper.pdf

- The exact number varies by source, but waters absorbs the erbium 2940nm wavelength 10-20 times more efficiently than it absorbs the CO2 10,600nm wavelength (I said 30 times)

- Clarification:  Eyelid skin is thinner closer to the lashes and on the medial aspect of the eyelid as compared to skin further from the lashes and the lateral aspect of the eyelid.  A study in Korean skin by Hwang et al found the thickest part of the eyelid to be just below the eyebrow (1.127 +/- 238um) with the thinnest skin near the ciliary margin 320 +/- 49um).  Jeong et al found that epidermal thickness is similar between genders while men had thicker reticular dermis than women and skin thickness was not correlated with BMI.

- The UV wavelengths range from 100nm - 400nm.  UVC: 100nm - 280nm; UVB: 280nm-315nm; UVA: 315-400.  (I used single wavelength numbers rather than a range for ease of explanation).

 

Citations for skin thickness:

Full thickness punch biopsies from cadaver heads processed with paraffin-embedded slides:

Karan Chopra, Daniel Calva, Michael Sosin, Kashyap Komarraju Tadisina, Abhishake Banda, Carla De La Cruz, Muhammad R. Chaudhry, Teklu Legesse, Cinithia B. Drachenberg, Paul N. Manson, Michael R. Christy, A Comprehensive Examination of Topographic Thickness of Skin in the Human Face, Aesthetic Surgery Journal, Volume 35, Issue 8, November/December 2015, Pages 1007–1013, https://doi.org/10.1093/asj/sjv079

 

Ultrasonographic measurements in live participants:

Jeong KM, Seo JY, Kim A, Kim YC, Baek YS, Oh CH, Jeon J. Ultrasonographic analysis of facial skin thickness in relation to age, site, sex, and body mass index. Skin Res Technol. 2023 Aug;29(8):e13426. doi: 10.1111/srt.13426. PMID: 37632182; PMCID: PMC10370326.

 

Cut and trichrome stained specimens from fresh cadavers

Hwang, Kun MD, PhD*; Kim, Dae Joong PhD†; Hwang, Se Ho†. Thickness of Korean Upper Eyelid Skin at Different Levels. Journal of Craniofacial Surgery 17(1):p 54-56, January 2006. | DOI: 10.1097/01.scs.0000188347.06365.a0