Dermoscopy (dermatoscopy, epiluminescence microscopy) is a non-invasive technique that uses magnification (typically 10x) and either polarized or non-polarized light to visualize subsurface skin structures not visible to the naked eye. By eliminating surface reflection and enabling visualization of the dermal-epidermal junction and superficial dermis, dermoscopy improves diagnostic accuracy for pigmented lesions by 20-30% compared to naked-eye examination. Optical principles: Non-polarized dermoscopy requires a liquid interface (gel, oil, or alcohol) between the lens and skin to eliminate surface refraction, allowing visualization of subsurface structures. Polarized dermoscopy uses cross-polarized light that penetrates the stratum corneum without a liquid interface, visualizing deeper dermal structures. Polarized dermoscopy reveals crystalline structures, shiny white streaks, and vascular patterns better than non-polarized. Some structures are best seen with non-polarized light (milia-like cysts, comedo-like openings in seborrheic keratoses). The two-step dermoscopic algorithm: Step 1 — Determine if the lesion is melanocytic or non-melanocytic (look for pigment network, aggregated globules, homogeneous blue pattern, or parallel pattern [acral]). Step 2 — If melanocytic, determine if it is benign, suspicious, or malignant using pattern analysis. Melanoma-specific dermoscopic structures: atypical pigment network...