Produced naturally by the body (and found in plants and minerals), silica is most concentrated in skin, hair, and fingernails, where it enhances collagen production to help strengthen locks and nails and keep skin supple and wrinkle-free. Supplementing with bioavailable, plant-derived silica (look for products such as EuroPharma’s Trica-Sil, derived from horsetail—the richest plant-based source) can help make up for age-related loss of collagen production and keep concentrations high in your key beauty areas. But the Environmental Working Group has linked some powdered silica to cancer and immune-system toxicity. Though most shadows and face powders contain harmless sand-derived silica, research products and companies to make sure they don’t use crystalline silica, which may contain potentially toxic crystalline quartz.