Expired makeup should not be used and should be disposed of for several reasons.

Firstly, over time, the chemical structure of makeup can change. This is due to factors such as exposure to air, light, and bacteria, which can degrade the product and reduce its efficacy. Using expired makeup can therefore lead to subpar results, as the product may not perform as it was initially designed to.

Secondly, expired makeup can pose a risk to your health. As makeup ages and degrades, it can become a breeding ground for bacteria. This is particularly concerning for products that come into contact with sensitive areas, such as the eyes and lips. Using expired makeup can lead to skin irritation, infections, and in severe cases, can even cause long-term damage.

Lastly, the preservatives in makeup, which are designed to prevent the growth of bacteria and extend the product's shelf life, also degrade over time. Once these preservatives are no longer effective, the product becomes unsafe to use.

In conclusion, it's best to throw out expired makeup. It's not worth the risk to your health or the diminished performance of the product. Always remember to check the expiration date of your makeup and replace it as necessary.