How often should foundation be replaced to guard against contamination?

Liquid foundation is perishable and should be replaced after six months. Powder foundation lasts up to a year and mineral foundation lasts indefinitely because it is inorganic. To help prevent contaminating liquid foundation, pour a small amount of foundation on the back of your clean hand or onto a clean dish. Avoid touching the foundation in the bottle with your hand. Use a clean, nylon foundation brush to apply foundation and wash after each use.