Cortisol is one of your body’s main hormones to keep things running smoothly—its key role is managing stress, but it also regulates blood pressure and keeps inflammation down.

Your cortisol levels also change throughout the day—they’re regulated by your body’s internal clock, called your circadian rhythm.

Cortisol tends to peak 30 to 45 minutes after you wake up. This surge is called the cortisol awakening response, when cortisol levels increase by 50% to 150%.

“(Cortisol) helps us get up in the morning,” said Richard Siegel, MDendocrinologist and co-director of the Diabetes and Lipid Center at Tufts Medical Center. “It mobilizes energy and helps with alertness.”

Not everyone experiences this cortisol awakening response. If someone typically works night shifts or if they regularly have sleep disturbances, this response might get thrown off. Though research is limited, it’s estimated that about 75% of healthy adults experience the cortisol awakening response.

After that morning peak, cortisol levels start to decline, often plummeting in the afternoon (this is why you sometimes feel an afternoon slump around 3 p.m.).

Eventually, cortisol reaches its lowest levels around midnight, while you’re asleep, allowing your body to rest and restore. But around 3 a.m., it starts rising again—and when you wake up, the whole cycle starts over.

Outside of the daily rise and fall, cortisol levels can also spike throughout the day in healthy people when confronted with physically or emotionally stressful situations.

This is sometimes called the body’s “fight or flight response.” Cortisol increases and provides your body with the energy it needs—through glucose and fatty acids—to deal with stressors.

Cortisol can also spike when you’re sick, to help induce an immune response.

Chronically high cortisol levels can be due to prolonged stresscertain medical conditions like Cushing’s syndromeand medications like high-dose steroids.

When cortisol levels stay highit can lead to:

• Weight gain
• Thin arms and legs
• Round face
• Increased fat around the base of your neck or between your shoulder blades
• Easy bruising
• Wide purple streaks on your stomach, breasts, hips, and under your arms
• Muscle weakness

If you’re experiencing any of these symptoms and feel concerned about high cortisol levels, it’s best to talk to a healthcare provider about getting a cortisol test.

Cortisol levels naturally rise and fall throughout the day—they’re at their highest shortly after you wake up, and lowest when you’re asleep. This is completely normal and an important part of your body’s natural rhythm.

According to Monica Flores, MDendocrinologist at Beth Israel Deaconess Medical Center, simply getting enough sleep, exercising, and eating well should help support your regular cortisol cycle.

Sometimes, stressors or illness can also spike cortisol throughout the day, or it can remain elevated due to chronic stress, or certain diseases or medications. If you’re concerned about potentially elevated cortisol levels, speak to a healthcare provider.