To the best of my knowledge, there are no states in the United States where it is illegal to hang an air freshener in a car. Air fresheners are a common car accessory used to help eliminate odors and create a more pleasant driving experience, and they are widely available for purchase at auto supply stores, gas stations, and other retailers.
That being said, there are some states that have restrictions on certain types of air fresheners, particularly those that emit strong fragrances or contain potentially harmful chemicals. For example, California has a law called Proposition 65 that requires companies to provide warning labels on products that contain chemicals known to cause cancer, birth defects, or other reproductive harm. This law applies to many household and automotive products, including some types of air fresheners.
In addition to state laws, there are also federal regulations governing the manufacture and sale of air fresheners. The Environmental Protection Agency (EPA) regulates air fresheners as a type of “fragrance product,” and requires manufacturers to adhere to certain labeling and ingredient disclosure requirements. The EPA also monitors air fresheners for potential health and environmental impacts, and has issued guidance on how to use these products safely and responsibly.
Overall, while there may be some restrictions on certain types of air fresheners in certain states, there are no states where it is illegal to hang an air freshener in a car. However, it is always a good idea to use these products responsibly and in accordance with manufacturer instructions, to ensure that you are not exposing yourself or others to potentially harmful chemicals or fragrances.