Cystine is a non-essential amino acid notable for strengthening the structural integrity of proteins, including those in hair, skin, and nails. Cystine is synthesized in the human body and can also be obtained through high-protein foods. It’s a key component of keratin, a fibrous protein found in skin, hair, and nails, contributing to their strength and resilience. Additionally, cystine plays a role in various metabolic processes and acts as an antioxidant. It’s also involved in the synthesis of other important molecules, such as glutathione, which is crucial for detoxification and immune system function. However, excess cystine due to its metabolic issues can lead to cystinuria, which can lead to the formation of kidney stones.