For some people, Fourth of July fireworks aren't reason to celebrate.

The random explosion of fireworks can trigger a startle response in people who have post-traumatic stress disorder (PTSD). The mental health condition develops in some people after they witness a shocking, scary or dangerous event.

These triggers can be sights, sounds or scents that remind them of the trauma in any way.

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For individuals who have witnessed gun violence or who have served in the military, fireworks may trigger their PTSD.

"Although the loud noise of the fireworks can itself be triggering of traumatic memories, typically it is the unpredictability of the explosion that activates the arousal system or sympathetic nervous system," says Todd K. Favorite, Ph.D., clinical assistant professor of psychiatry and director of the U-M Psychological Clinic.

Symptoms of PTSD may include:

• Extreme vigilance and arousal

• Nightmares or insomnia

• Negative changes in mood

• Intrusive thoughts of the trauma

• Avoidance or social isolation

People with PTSD typically are highly alert to any movement or change that could signal danger.

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"It is often hard for them to focus their attention, and they experience intrusive mental images or 'flashbacks' and thoughts about the trauma events," says Favorite. "They can become easily angered or reactive to perceived threats.

"It is also likely that their mood is anxious, depressed, angry or fearful," he says.

PTSD affects about 7% to 8% of the U.S. population, a number reflecting only a small portion of those who have gone through a traumatic experience.

A predisposition for anxiety or depression

Those with a family history or a predisposition for anxiety or depression, and one's psychological temperament, may influence the development and expression of PTSD symptoms.

When people are aware of fireworks displays in advance, they are not surprised by the explosions and are able to better prepare for them.

If you have PTSD, ask your neighbors to alert you if they plan to set off fireworks.

SEE ALSO: 8 Tips for a Safer Fourth of July Fireworks Show

This will give you time to prepare yourself for the fireworks by gathering any materials you may need to help you (such as headphones or blackout curtains), practice self-regulation techniques, or even distance yourself from the fireworks display.

It is important to keep in mind that PTSD is not a sign of psychological weakness.

"PTSD can happen to anyone who has gone through, or witnessed, a terrifying death or life- threatening experience," says Favorite. "However, most people who go through traumatic events may have temporary difficulty adjusting and coping, but with time and good self-care, they usually get better."

If the symptoms last for months or years and interfere with your day-to-day functioning, you may need further treatment.

Seeking help

The National Center for Telehealth and Technology and the Department of Veterans Affairs' National Center for PTSD have helped in the development of two free apps for smartphones to help people cope better with symptoms of anxiety, panic and PTSD. One app is called Virtual Hope Box and the other is PTSD Coach.

If you are struggling with PTSD and want confidential guidance, you can call the Substance Abuse and Mental Health Services Administration (SAMHSA) National Helpline at 1-800-662-HELP (4357), or if you experience suicidal thoughts along with your PTSD episodes, call the National Suicide Prevention Lifeline at 1-800-273-8255.