Sheikh Salman al-Oadah
A healthy person may refrain from fasting if he has well-grounded fears that fasting will make him ill, subject him to severe difficulties, or place unbearable demands upon his person.
Ibn `Abbâs permitted breaking the fast for someone “…who suffers from severe and chronic thirst”. Some people suffer from chronic thirst and cannot go for long periods of time without water. Such people can break their fasts.
Ahmad b. Hanbal was asked about fasting for a very young girl who attains puberty and menstruates during the month of Ramadan. He replied: “She should fast, and if it is difficult for her, she should break her fast and make the missed days up later.”
Ahmad’s fatwâ takes into consideration the girl’s young age as well as her not being accustomed to fasting. It also takes into consideration that she may be beset by weakness in those circumstances.
Though Ahmad stated that she should make up her fast, his students did not mention that she had to do so in that particular situation.
And Allah knows best.
Source: Islam Today