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Higher harmonic generation microscopy (HHGM), combining both second- and third-harmonic generation (SHG and THG) modalities, is a new paradigm for in vivo noninvasive virtual biopsy. With the ability to achieve noninvasiveness, high resolution, and high penetrability at the same time, HHGM is a promising tool for future noninvasive diagnosis of skin diseases. In this paper, we report our preliminary pilot clinical trial results on in vivo virtual biopsy of human skin by using HHGM. In vivo virtual biopsy imaging has been performed on 21 volunteers' inside and outside forearm skin along with the damage evaluation. Together with an embryo viability study, our results not only indicate a superior viability performance of the developed system, but also a much improved penetrability in different skin types. Ex vivo studies further confirm the capability of the developed virtual biopsy system to pathohistologically distinguish different skin diseases. Our in vivo HHGM biopsy study of human skin with different colors also reveals the central role of melanin in the epi-THG resonance enhancement and attenuation. With a unique capability to molecular image the melanin distribution, epi-THG microscopy is also highly valuable for diagnosing and screening early melanocytic lesions.