Each state has different laws regulating the operation of motorcycles, and a conscientious motorcyclist will consider these differences when traveling over state lines. The American Motorcyclist Association has a useful tool that allows people to search motorcycle laws by each state: http://www.americanmotorcyclist.com/Rights/State-Laws.aspx
In Indiana, motorcyclists are not required to wear safety helmets if they 18 years or older. However, safety helmets as well as protective glasses, goggles, or face shield are required to be worn by motorcyclists under the age of 18. See Ind. Code 9-19-7-1. Although safety helmets are an important part of protective gear and should be worn, the legal significance of Indiana’s law means that in most circumstances, if an adult motorcyclist who is not wearing a helmet is injured in an accident with another motor vehicle, the motorcyclist not wearing a helmet cannot be shown to be comparatively at fault merely because he or she was not wearing a helmet.