Spermidine solution is widely used in cell culture and molecular biology research due to its role in promoting cell growth, proliferation, and autophagy. It is commonly added to culture media to support the growth of certain mammalian cells and microorganisms that require polyamines for optimal development. In aging and longevity studies, spermidine is applied to induce autophagy, a cellular recycling process linked to extended lifespan in model organisms. It is also used in epigenetic research, as spermidine influences chromatin structure and gene expression by serving as a precursor for post-translational modifications of histones. In addition, spermidine solutions are utilized in cryopreservation protocols to protect cells during freezing and thawing processes. Due to its antioxidant properties, it finds application in cosmetic formulations aimed at skin rejuvenation and protection against oxidative stress. Some dietary and nutraceutical products use spermidine solutions as active ingredients, targeting cognitive health and metabolic function.