Assalaamu Alaikum. If a person suffers from primary hyperhidrosis (meaning that they sweat excessively); it is a genetic and hereditary disease, is fasting still compulsory on them. When fasting, they feel weak and thirsty and dehydrated. Is it allowed for them to skip some fasts in between? And they would do the Qadha after Ramadan intermittently. The problem is something that they have no control over. And treatments for it have side-effects that much, much worse than the problem itself.
Wa Alaikum Assalaam,
Fasting will still be compulsory upon the person in this state. Such a person must begin the fast in the morning with the firm intention to observe the fast. If, during the day, the person becomes so thirsty and dehydrated that continuing the fast becomes unbearable, then one will be allowed to break the fast at that time to save oneself from severe harm.
The missed fasts will have to be made up after Ramadhan when it is easy for the person to do so. Therefore, the person should begin the fast every day. He must not neglect the fast from the morning. He must start the fast from the morning. Then, during the day, the person will assess himself. If the fast can be continued without severe hardships, it must be kept until the time of sunset. If he cannot continue, on account of the problem as mentioned before, then the person can break the fast and make up for the days afterwards.
And Allah Knows Best.
Mufti Waseem Khan.
This answer was collected from DarulUloomTT.net, which is operated under the supervision of Mufti Waseem Khan from Darul Uloom Trinidad and Tobago.