But many people may not be aware that those celebrations could affect others in a negative way. Whether it's the booming sounds, bright sights, or even the burning smell fireworks can cause nightmares, flashbacks and anxiety in those with PTSD who fought for those freedoms we're celebrating. "Smells in particular, that old factory system, our sense of smell and our connections to the brain, that's very powerful. And then when a person smells those smells again - which may be many years later - that can often activate those traumatic memories to rush back and cause a powerful anxiety response in the individual," said Dr. Robert Connell, acting associate chief of staff for mental health services with the Montana VA Health Care System (MTVAHCS).