Expired makeup can have a significant impact on sensitive skin, and it's not just about the product losing its effectiveness. The primary concern is the potential for bacterial growth in expired makeup, which can lead to skin infections, irritation, and allergic reactions.

When makeup expires, the preservatives that prevent microbial growth start to break down, making the product a breeding ground for bacteria and fungi. These microbes can cause various skin problems, including acne, redness, swelling, and even more severe infections.

Sensitive skin is particularly vulnerable because it typically has a weakened barrier function. This means that it's less able to defend itself against potential irritants, allergens, and pathogens, including those found in expired makeup.

Moreover, the chemical stability of the ingredients in makeup can also change over time. This can lead to the formation of substances that can irritate the skin or cause allergic reactions. For example, certain pigments can degrade into substances that are potentially harmful.

Finally, expired makeup can also lose its original properties. For instance, sunscreens may no longer provide the promised level of UV protection, and moisturizing agents may not be as effective, leaving the skin unprotected and more susceptible to damage.

Therefore, it's crucial to pay attention to the expiration dates of your makeup products, especially if you have sensitive skin. Always store your makeup properly, in a cool, dry place, and avoid sharing makeup to prevent cross-contamination.