Thanks for your query.
The commonest cause is the development of the gas producing bacteria in the butt area, special glands and nothing serious about unless there is development of any other problems.
You can keep the area clean off the sweat and so, by regular bathing, keeping the parts clean and tidy and apply liquid Povidone Iodine 2 times a day.
your problem may be solved completely.
You will have to maintain the personal hygiene and your problems may be solved.
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