context: When you have posttraumatic stress disorder ( PTSD), your symptoms can come and go. You might feel fine until you hear a car backfire loudly. Suddenly, you become very afraid. Images of your time fighting in a war flood back. Certain triggers can set off your PTSD. They bring back strong memories. You may feel like you're living through it all over again. Triggers can include sights, sounds, smells, or thoughts that remind you of the traumatic event in some way. Some PTSD triggers are obvious, such as seeing a news report of an assault. Others are less clear. For example, if you were attacked on a sunny day, seeing a bright blue sky might make you upset. Knowing your triggers can help you better cope with your PTSD. When faced with danger, your body gets ready to fight, flee, or freeze. Your heart beats faster. Your senses go on high alert. Your brain stops some of its normal functions to deal with the threat. This includes your short-term memory. With PTSD, your brain doesn't process the trauma the right way. It doesn't file the memory of the event as being in the past. The result: You feel stressed and frightened even when you know you're safe. The brain attaches details, like sights or smells, to that memory. These become triggers. They act like buttons that turn on your body's alarm system. When one of them is pushed, your brain switches to danger mode. This may cause you to become frightened and your heart to start racing. The sights, sounds, and feelings of the trauma may come rushing back. This is called a flashback. Anything that reminds you of what happened right before or during a trauma is a potential trigger. They're usually tied to your senses. You may see, feel, smell, touch, or taste something that brings on your symptoms. While triggers themselves are usually harmless, they cause your body to react as if you're in danger. A number of things can trigger your PTSD. Some of the most common include: People: Seeing a person related to the trauma may set off a PTSD reaction. Or someone may have a physical trait that's a reminder. For example, if someone with a beard mugged you, other bearded men may bring back memories. Thoughts and emotions: The way you felt during a traumatic event (afraid, helpless, or stressed) could cause symptoms. Things: Seeing an object that reminds you of the trauma can cue your PTSD symptoms. Scents: Smells are strongly tied to memories. For instance, someone who survived a fire might become upset from the smoky smell of a barbecue. Places: Returning to the scene of a trauma is often a trigger. Or a type of place, like a dark hallway, may be enough to bring on a reaction. TV shows, news reports, and movies: Seeing a similar trauma often sets off symptoms. This includes scenes from a television show or movie, or a news report. Feelings: Some sensations, such as pain, are triggers. For survivors of assault, a touch on a certain body part may lead to a flashback. Sounds: Hearing specific noises, songs, or voices may bring back memories of the trauma. For example, hearing a car backfire may remind a veteran of gunfire. Tastes: The taste of something, like alcohol, may remind you of a traumatic event. Situations: You may tie scenarios with the trauma. For instance, being stuck in an elevator might remind you of feeling trapped after a car accident. Anniversaries: It's often hard to go through a date marked by trauma without remembering it, as is the case for many survivors of the terrorist attacks on September 11, 2001. Words: Reading or hearing certain words could cue your PTSD. Some are obvious. Others are subtle. In fact, you may not realize something is a trigger until you have a reaction. It may seem like your PTSD symptoms come out of the blue. But they're usually caused by an unknown trigger. Feeling as if you're in danger is a sign that you've experienced a PTSD trigger. A therapist can help you identify yours. He can also help you learn ways to cope.