Absolutely, using expired makeup can be detrimental to your skin health. As a cosmetic scientist, I can tell you that makeup products, like any other consumer goods, have a shelf life. This shelf life is determined by the stability of the ingredients, the packaging, and the preservatives used in the formulation.

When makeup products expire, the preservatives that keep bacteria and fungi at bay start to break down, making the product a breeding ground for harmful microorganisms. This can lead to skin irritations, rashes, blemishes, and even severe infections in some cases.

Moreover, over time, the chemical structure of some ingredients may change, causing them to lose their effectiveness. For instance, the pigments may start to separate, the product may dry out, or the consistency may change, affecting the product's performance and potentially causing harm to your skin.

In addition to this, certain makeup products like mascara and eyeliner come into direct contact with your eyes. Using expired products can lead to serious eye infections.

Therefore, it's crucial to pay attention to the expiration dates on your makeup products and replace them regularly to maintain your skin's health and integrity. It's always better to be safe than sorry when it comes to skincare.