Sweating often messes up a perm because sweat is a form of moisture that can loosen layers of the hair. Consequently, moisture causes hair to be frizzy. When the chemicals used in a hair perm are combined with sweat, the result can be a sour odor.
The primary reason why people who get their hair permed need to wait three days before getting it wet is because permed hair needs time to normalize and stabilize. Avoiding moisture also reduces the chances of damaging the hair. In the case of sweating, people who have more alkaline in their sweat tend to loose their curls more easily.