Of course there are some disadvantages of using helment. Our head won't be getting fresh air. We could not hear if we wear helment. It is little uncomfortablewhile ridding. Sometimes, it sweat inside which dirties the helment as well as our head. The most important disadvantages of wearing the helment is the cause of dandruff and loss of hairs. This is the most issue problem where riders are facing while wearing helment. Fortunately designer are coming out with the new idea of making vents and holes in the helment for making the circulation of air inside. If there is a smooth flow air around your head, then will be feel comfortable. But I am not sure that  such helmets are out in the market or not. Even there are disadvantages of wearing a helment, we should practise the habits of wearing helments. After all, our life is the most important reason for us to live in the world.