The chemical reaction that occurs when you are frightened is called the "fight or flight" response. This response is triggered by the release of hormones such as adrenaline and cortisol from your adrenal glands. These hormones cause your body to go into "high alert" mode, which prepares you to either face a threat or flee from it.

Here is a more detailed look at the chemical reactions that occur during the fight or flight response:

* Adrenaline: Adrenaline is a hormone that is produced by your adrenal glands. It is also known as epinephrine. When you are frightened, your adrenal glands release adrenaline into your bloodstream. This causes your heart rate to increase, your blood pressure to rise, and your breathing to quicken. Adrenaline also dilates your airways and pupils, which allows you to take in more oxygen and see more clearly.

* Cortisol: Cortisol is another hormone that is produced by your adrenal glands. It is also known as the "stress hormone." Cortisol helps your body to convert food into energy, and it also suppresses the immune system. This allows you to focus all of your energy on dealing with the threat at hand.

* Endorphins: Endorphins are hormones that are produced by your brain. They are also known as "feel-good" hormones. When you are frightened, your brain releases endorphins to help you cope with the stress of the situation. Endorphins can also help to relieve pain and inflammation.

The fight or flight response is a natural defense mechanism that helps you to stay safe in dangerous situations. However, if this response is triggered too often, it can lead to health problems such as anxiety, depression, and heart disease.