Cystatin D is a protein that belongs to the cystatin family, which plays a crucial role in regulating the activity of enzymes called cysteine proteases. These enzymes are involved in various biological processes, including protein degradation and immune responses. Cystatin D is primarily produced in the human body and is found in various tissues, including the skin and brain. Research has shown that Cystatin D may have implications in several health conditions, such as neurodegenerative diseases and inflammatory disorders. Its levels can be affected by different factors, including age and disease states, making it a potential biomarker for certain medical conditions.