Caffeine is a diuretic, which means that it can increase urine production and lead to dehydration. Dehydration can cause the vocal cords to become dry and inflamed, leading to hoarseness, throat irritation, and difficulty singing. In severe cases, dehydration can even cause vocal cord damage.
It is important for singers to stay hydrated, especially before and during performances. This means drinking plenty of water and avoiding caffeine and other diuretics. While a small amount of caffeine may not be harmful, it is best to consume it in moderation to avoid any negative effects on the voice.