What can be an effect of using outdated nail products?

Using outdated nail products can lead to possible allergic reactions due to changes in the chemical composition or stability of the product over time. When nail products expire or reach their shelf life, the ingredients may break down or separate, which can result in irritants or allergens being present in the product. This can make it difficult for a nail technician to ensure a safe and predictable application, as the body may react negatively to these compromised ingredients.

In contrast, the other options suggest outcomes that are typically associated with high-quality or fresh products. Improved color vibrancy, safe application, and enhanced durability are usually characteristics of fresh, valid formulations but cannot be guaranteed with outdated products, which pose significant risks rather than benefits.