High-Intensity vs. High-Power Laser Therapy: Biophysical Implications of a Semantic Ambiguity and the Distinct Role of Photoacoustic Effects

Words matter in science, particularly when they define technologies with distinct biological mechanisms. High-Intensity Laser Therapy (HILT) is often conflated with High-Power Laser Therapy or High-Level Laser Therapy (HPLT/HLLT), despite these terms referring to laser systems with fundamentally different physical properties and therapeutic effects. While many therapeutic lasers can elicit photochemical and photothermal effects, only devices delivering high-peak, short-duration pulses at very low duty cycles are able to generate acoustic pressure waves, which are characteristic of true HILT systems. These photoacoustic effects uniquely activate mechanotransduction pathways involved in cellular differentiation, extracellular matrix remodeling, and long-term tissue regeneration. This review highlights the widespread misclassification in the laser therapy literature, where devices lacking genuine photoacoustic capabilities are often incorrectly described as HILT. Such semantic ambiguity not only undermines biological specificity, but also inflates clinical claims, misleading practitioners, and obscures the comparative interpretation of clinical studies. Within the laser science community, it is widely recognized that average power alone is insufficient to characterize a therapeutic mechanism of laser therapies, as it does not provide insight into ability to generate pressure waves. To resolve these issues, we propose a mechanism-based classification that clearly distinguishes photochemical, photothermal, and photoacoustic effects. We further provide a quantitative comparison showing that systems delivering the same total energy produce peak parameters that differ by orders of magnitude depending on duty-cycle architecture, reinforcing the need for mechanism-based classification. We also advocate for greater rigor in reporting technical parameters such as peak power, pulse duration, and duty cycle. By ensuring proper terminology and transparent reporting, this framework will advance scientific rigor, facilitate accurate comparisons across studies, and improve the clinical application of regenerative medicine therapies.