Defining Safe Light Intensity Limits of Near-Infrared Illumination Avoiding Skin Heating in Medical Optical...

Area of Science:

• Biomedical Optics
• Dermatology
• Thermal Physiology

Background:

• Near-infrared (NIR) illumination is used in various medical and cosmetic applications.
• Understanding the thermal effects of NIR on human skin is crucial for safety.
• Skin tone variations can influence light absorption and thermal response.

Purpose of the Study:

• To quantify skin heating under different near-infrared illumination intensities.
• To identify safe exposure thresholds for various skin tones and illumination methods.
• To compare thermal responses between free-beam and dermal probe NIR delivery.

Main Methods:

• In vivo study on human participants with skin tones 1-5.
• Near-infrared (764 nm) illumination delivered via free laser beam and dermal diffusive probe.
• Measurement of skin temperature increases under varying irradiance levels.

Main Results:

• Skin tone significantly affected heating under free-beam illumination.
• Dermal probe illumination showed no significant dependence on skin tone.
• Maximum safe irradiance limits were established: 7.6 mW/mm² (free-beam) and 2.3 mW/mm² (dermal probe).
• These limits correspond to a maximum skin temperature of 43°C.

Conclusions:

• Safe exposure thresholds for near-infrared illumination vary by delivery method and are influenced by skin tone for free-beam applications.
• Established safety limits are applicable to skin tones 1-5.
• Further research is needed for skin tone 6 to establish comprehensive safety guidelines.