Multispectral short-wave infrared imaging for characterization of skin fluid content independent of skin pigmentation

Clinical assessment of inflammatory skin disease relies heavily on visual cues such as erythema, yet this sign is often less conspicuous in darkly pigmented skin because epidermal melanin attenuates visible reflectance and reduces lesion–background contrast. Short-wave infrared (SWIR, 1000–1700 nm) imaging probes a spectral window in which water absorption is strong and melanin absorption is weak, suggesting a pigment-insensitive approach to visualizing inflammation-associated dermal fluid. Here we develop a portable cross-polarized multispectral visible-to-SWIR imaging system and pseudocolor reconstruction method to enhance fluid contrast. In 24 healthy volunteers spanning a wide range of objectively measured pigmentation (individual typology angle ITA −46° to +45°), visible reflectance varied strongly with pigmentation, whereas SWIR reflectance was largely independent of skin tone. Following intradermal saline injection as a model of localized inflammation-associated dermal fluid, pseudocolor SWIR imaging markedly increased lesion-to-background contrast compared with co-registered color photography (∆E 50.2±16.7 vs 2.00±1.35; p=5.9×10⁻¹³) without correlation between SWIR contrast and pigmentation. In pilot subjects with acne, SWIR imaging enhanced lesion visibility across pigmentation levels and revealed clinically occult inflammation in darkly pigmented skin. These findings establish multispectral SWIR imaging as a quantitative, pigment-insensitive strategy for visualizing cutaneous inflammation.