If people didn’t feel fear, they wouldn’t be able to protect themselves from legitimate threats. Fear is a vital response to physical and emotional danger that has been pivotal throughout human evolution, but especially in ancient times when men and women regularly faced life-or-death situations.

Today, the stakes are lower, but while public speaking, elevators, and spiders don’t present the same type of immediately dire consequences that faced early man, some individuals still develop extreme fight-flight-or-freeze responses to specific objects or scenarios.

Many people experience occasional bouts of fear or “nerves” before a flight, first date, or big game. But when someone’s fear is persistent and specific to certain threat, and impairs his or her everyday life, that person might have what’s known as a specific phobia.

At least 60 percent of adults admit to having at least one unreasonable fear, although research to date is not clear on why these fears manifest. One theory is that humans have a genetic predisposition to fear things that were a threat to our ancestors, such as snakes, spiders, heights, or water, but this is difficult to verify, although people who have a first-degree relative with a specific phobia appear more likely to have the same one. Others point to evidence that individuals fear certain things because of a previous traumatic experience with them, but that fails to explain the many fears without such origins.

Personality traits such as neuroticism appear to increase one’s likelihood of developing a phobia, and a tendency toward frequent worries and negative thoughts may also increase the risk, as may being raised by overprotective parents, losing a parent, or sexual or physical abuse. Most likely is that people follow multiple pathways to fears, not least among them the emotional response of disgust.

Fear is a human emotion that is triggered by a perceived threat. It is a basic survival mechanism that signals our bodies to respond to danger with a fight or flight response. As such, it is an essential part of keeping us safe.

However, when people live in constant fear, whether from physical dangers in their environment or threats they perceive, they can experience negative impacts in all areas of their lives and even become incapacitated.

How fear works

Fear prepares us to react to danger. Once we sense a potential danger, our body releases hormones that:

• Slow or shut down functions not needed for survival (such as our digestive system)
• Sharpen functions that might help us survive (such as eyesight). Our heart rate increases, and blood flows to muscles so we can run faster.

Our body also increases the flow of hormones to an area of the brain known as the amygdala to help us focus on the presenting danger and store it in our memory.

Cortisol is a glucocorticoid hormone that your adrenal glands produce and release.

Hormones are chemicals that coordinate different functions in your body by carrying messages through your blood to your organs, skin, muscles and other tissues. These signals tell your body what to do and when to do it.

Glucocorticoids are a type of steroid hormone. They suppress inflammation in all of your bodily tissues and control metabolism in your muscles, fat, liver and bones. Glucocorticoids also affect sleep-wake cycles.

Your adrenal glands, also known as suprarenal glands, are small, triangle-shaped glands that are located on top of each of your two kidneys. They’re a part of your endocrine system.

Cortisol is an essential hormone that affects almost every organ and tissue in your body. It plays many important roles, including:

• Regulating your body’s stress response.
• Helping control your body’s use of fats, proteins and carbohydrates, or your metabolism.
• Suppressing inflammation.
• Regulating blood pressure.
• Regulating blood sugar.
• Helping control your sleep-wake cycle.

Your body continuously monitors your cortisol levels to maintain steady levels (homeostasis). Higher-than-normal or lower-than-normal cortisol levels can be harmful to your health.

Cortisol is widely known as the “stress hormone.” However, it has many important effects and functions throughout your body aside from regulating your body’s stress response.

It’s also important to remember that, biologically speaking, there are multiple different kinds of stress, including:

• Acute stress: Acute stress happens when you’re in sudden danger within a short period of time. For example, barely avoiding a car accident or being chased by an animal are situations that cause acute stress.
• Chronic stress: Chronic (long-term) stress happens when you experience ongoing situations that cause frustration or anxiety. For example, having a difficult or frustrating job or having a chronic illness can cause chronic stress.
• Traumatic stress: Traumatic stress happens when you experience a life-threatening event that induces fear and a feeling of helplessness. For example, experiencing an extreme weather event, such as a tornado, or experiencing war or sexual assault can cause traumatic stress. In some cases, these events can lead to post-traumatic stress disorder (PTSD).

Your body releases cortisol when you experience any of these types of stress.

Almost all tissues in your body have glucocorticoid receptors. Because of this, cortisol can affect nearly every organ system in your body, including:

• Nervous system.
• Immune system.
• Cardiovascular system.
• Respiratory system.
• Reproductive systems (female and male).
• Musculoskeletal system.
• Integumentary system (skin, hair, nails, glands and nerves).

More specifically, cortisol affects your body in the following ways:

Regulating your body’s stress response: During times of stress, your body can release cortisol after releasing its “fight or flight” hormones, such as adrenaline, so you continue to stay on high alert. In addition, cortisol triggers the release of glucose (sugar) from your liver for fast energy during times of stress.

Regulating metabolism: Cortisol helps control how your body uses fats, proteins and carbohydrates for energy.

Suppressing inflammation: In short spurts, cortisol can boost your immunity by limiting inflammation. However, if you have consistently high levels of cortisol, your body can get used to having too much cortisol in your blood, which can lead to inflammation and a weakened immune system.

Regulating blood pressure: The exact way in which cortisol regulates blood pressure in humans is unclear. However, elevated levels of cortisol can cause high blood pressure, and lower-than-normal levels of cortisol can cause low blood pressure.

Increasing and regulating blood sugar: Under normal circumstances, cortisol counterbalances the effect of insulin, a hormone your pancreas makes, to regulate your blood sugar. Cortisol raises blood sugar by releasing stored glucose, while insulin lowers blood sugar. Having chronically high cortisol levels can lead to persistent high blood sugar (hyperglycemia).

Helping control your sleep-wake cycle: Under regular circumstances, you have lower cortisol levels in the evening when you go to sleep and peak levels in the morning right before you wake up.

 This suggests that cortisol plays a significant role in the initiation of wakefulness and plays a part in your body’s circadian rhythm.

Optimum cortisol levels are necessary for life and for maintaining several bodily functions. If you have consistently high or low cortisol levels, it can have negative impacts on your overall health.