Selective photothermolysis to target sebaceous glands: Theoretical estimation of parameters and preliminary results using a free electron laser

Abstract

The success of permanent laser hair removal suggests that selective photothermolysis (SP) of sebaceous glands, another part of hair follicles, may also have merit. About 30% of sebum consists of fats with copious CH(2) bond content. SP was studied in vitro, using free electron laser (FEL) pulses at an infrared CH(2) vibrational absorption wavelength band. Absorption spectra of natural and artificially prepared sebum were measured from 200 to 3,000 nm, to determine wavelengths potentially able to target sebaceous glands. The Jefferson National Accelerator superconducting FEL was used to measure photothermal excitation of aqueous gels, artificial sebum, pig skin, human scalp, and forehead skin (sebaceous sites). In vitro skin samples were exposed to FEL pulses from 1,620 to 1,720 nm, spot diameter 7-9.5 mm with exposure through a cold 4°C sapphire window in contact with the skin. Exposed and control tissue samples were stained using H&E, and nitroblue tetrazolium chloride staining (NBTC) was used to detect thermal denaturation. Natural and artificial sebum both had absorption peaks near 1,210, 1,728, 1,760, 2,306 and 2,346 nm. Laser-induced heating of artificial sebum was approximately twice that of water at 1,710 and 1,720 nm, and about 1.5× higher in human sebaceous glands than in water. Thermal camera imaging showed transient focal heating near sebaceous hair follicles. Histologically, skin samples exposed to ~1,700 nm, ~100-125 milliseconds pulses showed evidence of selective thermal damage to sebaceous glands. Sebaceous glands were positive for NBTC staining, without evidence of selective loss in samples exposed to the laser. Epidermis was undamaged in all samples. SP of sebaceous glands appears to be feasible. Potentially, optical pulses at ~1,720 or ~1,210 nm delivered with large beam diameter and appropriate skin cooling in approximately 0.1 seconds may provide an alternative treatment for acne.