Lasers are used in a growing number of medical and imaging applications, from surgery to photoacoustic imaging. To protect patients, safety guidelines define the maximum amount of laser energy that can be delivered to the skin without causing injury. However, these limits do not account for differences in skin pigmentation.
Because melanin absorbs light, skin with higher melanin levels may absorb more laser energy and generate more heat. Researchers have long suspected that skin tone could influence the risk of laser-induced injury, but experimental evidence has been limited.
Testing laser safety across skin tones
As reported in the Journal of Biomedical Optics , researchers from Johns Hopkins University measured how skin pigmentation affects the amount of laser energy required to cause visible skin injury. Their findings provide quantitative evidence that could help improve future laser safety guidelines and support the development of safer optics-based technologies.
The researchers conducted experiments using three Yucatan miniature pigs with different levels of skin pigmentation, ranging from very light to dark. Before laser exposure, they measured skin pigmentation using a colorimeter to calculate a melanin index and also recorded skin redness, or erythema, which can indicate inflammation after laser exposure.
The animals were exposed to single laser pulses at a wavelength of 750 nanometers. The pulses lasted five nanoseconds and covered a range of energy levels. The researchers evaluated 150 skin sites, examining them before exposure, immediately afterward, five minutes later, and one hour later. Photographs and colorimetric measurements were used to identify visible injury and quantify changes in skin redness.
By analyzing these observations, the researchers determined the ED 50 threshold, the laser energy expected to produce visible injury in 50 percent of exposed sites. They then used the results to examine how pigmentation influences the skin's response to laser exposure.
Darker skin showed lower injury thresholds
The study found that skin with higher melanin levels required substantially less laser energy to produce visible injury. Under the conditions tested, darkly pigmented skin reached the injury threshold with 27.7 percent less radiant exposure than lightly pigmented skin.
These results suggest that melanin plays a significant role in determining how much laser energy skin can safely tolerate. The findings also indicate that current safety limits may not fully capture biological differences related to skin pigmentation.
Toward more inclusive laser safety standards
The researchers say the work provides an experimental foundation for understanding how pigmentation affects laser-induced injury. Incorporating this knowledge into future safety models could help establish exposure limits that better reflect the diversity of human skin tones.
Such improvements could benefit technologies that rely on laser light, including photoacoustic imaging, where allowable laser exposure directly influences image quality and diagnostic performance. A better understanding of pigmentation-dependent injury thresholds may ultimately help reduce the risk of skin damage while enabling higher-performing medical imaging systems.
For details, see the original Gold Open Access article by J. Arroyo et al., “ Pigmentation-dependent skin injury thresholds with nanosecond single-pulse laser exposure, ” J. Biomed. Opt. 31(8), 085001 (2026), doi: 10.1117/1.JBO.31.8.085001
Journal of Biomedical Optics
Pigmentation-dependent skin injury thresholds with nanosecond single-pulse laser exposure
8-Aug-2026