Hana Kamkar, a famous singer, removed her hijab

The best protection is a good posture and sound vocal technique. Voices always need to be supported by the bigger muscles in the body - poor posture can lead to muscular tension and vocal strain. There are also other factors which might be less obvious.

Singers need to keep their bodies hydrated, so that the delicate vocal folds (or cords) can be kept supple. They would probably drink between two and three litres of water spread out throughout the day. The water would be at room temperature, rather than ice-cold.