Perspiration can definitely create problems for hearing aids. Manufacturers have worked hard to advance technology to improve the water resistance of hearing aids, but moisture will always be a problem. Try wearing a sweat band when you are engaged in physical activity. It will help soak up any excess moisture.
Hearing aids are just like any delicate electronic; you should always try to avoid putting them in a warm, humid environment. If you perspire a lot because of your job or where you live, you may want to get a specially designed hearing aid dryer (dry and store) or dehumidifier. This could be as simple as a small container with a desiccant pad or as advanced as an electronic case with drying and sanitizing functions. Storing your hearing aids in a dryer when you are not wearing them is a good way to extend the life of your hearing aid.
Try to keep your hearing aids clean and well maintained. Removing wax or other buildup will also help prevent moisture from penetrating the electronics. If you live in an area with high humidity, heat or pollen, you may also want to visit your hearing healthcare provider more frequently for a thorough cleaning.