A Compact Optical Sensor to Self‐Assess Skin Health after Sun Exposure

Abstract Excessive sun exposure is the major environmental risk factor for melanoma and other types of skin cancer. Reducing cumulative exposure to ultraviolet (UV) radiation and avoiding repeated, sporadic episodes of acute photodamage can drastically lower this risk. Photodamage after sun exposure can be assessed by monitoring erythema – skin redness – and increased pigmentation, both key indicators of excessive UV exposure. In this work, a compact optical device designed to monitor changes in pigmentation and erythema through reflectance measurements using four micro‐LEDs is presented, emitting at 405, 572, 650, and 700 nm, and a photodiode with extended visible‐near infrared sensitivity. Monte Carlo simulations are conducted to optimize the device design by evaluating light penetration into skin tissue as a function of source‐to‐detector distance to target key chromophores. The device is validated using skin‐mimicking tissue phantoms containing coffee, with similar optical properties to melanin, and hemoglobin to simulate changes in pigmentation and erythema, respectively. Using a signal‐to‐noise ratio threshold of 2, it is able to detect changes in pigmentation as small as 5% across all phototypes and erythema changes in lighter skin tones. This miniaturized device shows potential for personalized skin monitoring in therapeutic, cosmetic, and diagnostic applications.