What is cortisol? All about the 'stress hormone' and what it does for the body

When our bodies are under stress, either physical (like an injury) or psychological (like relationship struggles), our bodies go through an intense hormonal and neurological response – most commonly known as the fight-or-flight reflex. It's also referred to as sympathetic nervous system activation, or the HPA axis.

Your body responds to stress by releasing a steroid hormone called cortisol – sometimes called “the stress hormone.”

So what is cortisol, and what does it do to our bodies? We spoke with Dr. Megan Gunnar, PhD., a professor of developmental psychology at the University of Minnesota and The Institute of Child Development, to answer some of the most common questions about cortisol.

What is cortisol?

Although cortisol is known for its role in the stress response, it has many functions.

“Cortisol does so many things,” Gunnar begins. “It’s a steroid hormone, and steroid hormones have a particular structure that allows them to be what’s called lipid soluble, which means they don’t need to be actively transported into cells. Once they are in our cells, they travel up to the nucleus, where they get actively transported to genes that are responsive to them – and almost all cells are responsive. This is how they play a role in the transcription of genes. That is why cortisol does a lot of different things because it’s regulating a lot of different genes.”

In other words, cortisol affects almost every tissue and organ in our bodies.

What does cortisol do to the body?

“We produce cortisol every day. We produce it according to a daily rhythm where our levels begin to rise in the last hours of sleep. They reach their peak levels about 30 to 40 minutes after we wake up. Then, they decrease until they’re almost nothing. In fact, it needs to be almost nothing about an hour or so after we fall asleep so you can sleep well at night,” explains Gunnar. She adds, “Cortisol does a lot of different things early in the morning, like stimulating your interest in getting up and out, in grappling with novelty and in finding carbohydrates. “It’s like your cup of coffee. It’s the ‘let’s get up and get going!’” Gunnar chirps.

When you experience stress, cortisol travels throughout the body to prepare it to take on the stressor.

The Cleveland Clinic explains, “During the fight-or-flight response, your body is trying to prioritize, so anything it doesn’t need for immediate survival is placed on the back burner. This means that digestion, reproductive and growth hormone production, and tissue repair are all temporarily halted. Instead, your body is using all of its energy on the most crucial priorities and functions.”

The American Institute of Stress describes five key symptoms of fight-or-flight system activation:

  • Rapid heartbeat

  • Rapid breathing (hyperventilation)

  • Pale or flushed skin

  • Dilated pupils

  • Trembling

What does chronically elevated cortisol do to your body?

Gunnar says, “One effect of chronic stress is that it flattens the natural cortisol rhythm. You can get a sort-of hypo-functioning system with a flat rhythm that might be a little too high at night. This can disrupt your sleep and disrupt the levels in the morning, and really disrupt your whole system.”

And while the development of certain mental health conditions is influenced by a number of factors, cortisol dysregulation may play a role. “It is a risk factor for all sorts of health and mental health conditions, but it also (depends on) the characteristics of an individual,” explains Gunnar.

The next time you’re feeling stressed out – you may have cortisol to blame. But also, the next time you wake up, refreshed from a good night’s sleep and ready to grab some breakfast – you can thank cortisol!

Read more about stress and your body here:

Explained: Your body's intense reaction to stress

Spot the symptoms: Chronic stress can be a serious problem

Is stress making you sick? Symptoms of stress-related illness, tips for stress management.

Feeling stressed? Tips for how to reduce stress in your daily life

This article originally appeared on USA TODAY: What is cortisol? How it reacts in your body and when it's too high