Subcutaneous Injection: What It Is and How to Give One Uses and Benefits #ghk GHK Cu is a naturally occurring peptide in human plasma that declines with age. When used in injections (usually subcutaneous), it can offer various benefits: Skin Rejuvenation and Anti Aging: For subcutaneous injections, using shorter needles (4 5mm) is the safest choice to ensure medication stays in the fatty layer and avoids muscle injury. A 4mm needle is ideal, minimizing pain while keeping Amazon.com: Skin Perfection Copper Peptide Serum GHK CU 1% for Face & Hair Copper Peptides for Skin, Hair, & Scalp 1% Blue Liquid for Face, Neck, Body, Scalp Multi Use Serum Booster with