1. Wear and tear reduced functionality
Hearing aids commonly are worn 12-16 hours daily, 365 days a year. They are worn directly on the skin having to ward off, sweat (which from one to the next might be quite acidic or alkaline), cosmetics or hair products. All these substances might find its way into the hearing aid through the battery compartment, damage switches or other mechanical components or block and damage microphones. Even if none of this happens, moisture in the form of humidity or condensation, caused by sudden changes in temperature, still could find its way into your hearing aids and cause damage or component deterioration.
Modern hearing aids are nano-coated and have many other systems to protect them from all of the above, but over time, even if these compounds do not damage your hearing aids immediately, they might gradually reduce the effectiveness of your hearing aids it.
This often is a bigger problem than if they suddenly stop altogether. Gradual reduction of the effectiveness might not be noticed and the benefits you are getting from your hearing aids will gradually and unnoticeable be reduced.
Often these problems are only discovered at a routine check-up. That is one of the reason why it is so important that you have your hearing aids checked every 3 months.