Caffeine impurities are unwanted substances that can be present in caffeine products. These impurities can come from various sources, including the manufacturing process, raw materials, or even environmental factors. Some common caffeine impurities include theophylline, theobromine, and chlorogenic acid. These impurities can have negative effects on the quality and safety of caffeine products, and must be carefully monitored and controlled to ensure the purity and efficacy of the final product.