His fasting is not invalidated; because this process does not involve entering anything into the stomach, and one only breaks the fast by what enters; as Ibn Abbas, may Allah be pleased with him, said: "Fasting is only broken by what enters, not by what exits"; and because it resembles cupping, and the Messenger of Allah, peace be upon him, was cupped while he was fasting. However, it is disliked for a fasting person unless there is a need, because it may weaken him for fasting and lead to breaking the fast.