Many people have experienced feelings of anxiousness at some point in their lives, whether the feelings were triggered by an important exam, a first date or unexpected bad news. For people with an anxiety disorder, these feelings can turn into recurring, intrusive thoughts or concerns that impact everyday life.

And according to the American Psychological Association, anxiety can also be categorized by physical symptoms.

Dr. Sai Achuthan, a consultant psychiatrist at Cygnet Health Care in the U.K., told Live Science that most of these symptoms are caused by the excessive production of stress hormones, including cortisol, adrenaline, noradrenaline and vasopressin. These hormones activate the body's fight or flight response, which triggers symptoms such as an increased heart rate, sweating and rapid breathing.

Live Science spoke to experts to learn more about some of the most common physical symptoms of anxiety and the mechanisms behind them.

Headaches

Migraines and chronic daily headaches are common in people who have an anxiety disorder, according to the Anxiety and Depression Association of America. The most common type of headache is a tension headache where the individual feels that there is a tight band around their head, Achuthan said.

Headaches can be triggered by the release of stress hormones, which can constrict blood vessels in the brain, said Dr. Anup Mathew, a lead psychiatrist at Cantourage Clinic in the U.K.

However, it is often difficult to determine which comes first: anxiety or headaches. "Headaches can be a part of anxiety symptoms or a headache can actually lead to anxiousness," Achuthan said.

Cardiovascular symptoms

People with anxiety often report cardiovascular symptoms, such as a tight chest or a pounding heart. This is because stress hormones can cause blood vessels to constrict, leading to high blood pressure and an increased heart rate, Mathew said.

Anxiety disorders have also been linked with impaired functioning of the vagus nerve — the body's superhighway that carries information between the brain and internal organs — and reduced heart rate variability (HRV) — the changes in time between heart beats — according to a 2014 review published in the journal Frontiers in Psychiatry. The vagus nerve plays a central role in regulating cardiac activity: When it doesn’t function properly, it can lead to the heart failing to contract in an efficient manner. Low HRV, meanwhile, predisposes an individual to slower recovery from stressors, the review researchers wrote.

Digestive symptoms

When an individual is anxious, more stress hormones enter their digestive system, Achuthan said. This can lead to digestive problems, such as bloating, abdominal pain, nausea and constipation.

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The link between anxiety and visceral hypersensitivity (low pain threshold in internal organs) may be caused by a combination of genetic factors and early life experiences, according to a 2017 review published in the journal Frontiers in Systems Neuroscience. Early childhood is a pivotal period for the development of brain circuits involved in regulating stress and pain. Certain genetic polymorphisms may increase the risk of these brain circuits not developing properly. When a genetically predisposed individual is subject to adverse early life experiences, such as trauma or abuse, their pain neurocircuitry may develop in a way that enhances feelings of pain and anxiety in adulthood.

Stress hormones can also disrupt the balance of bacteria in the gut, leading to inflammation and other digestive issues, Mathew said. A 2021 review published in the journal Clinical Psychology Review found that people with an anxiety disorder tend to have more pro-inflammatory bacteria (such as Enterobacteriaceae and Desulfovibrio), and fewer of the beneficial bacteria (such as Faecalibacterium).

Poor immunity

Cortisol, which is excessively produced during periods of anxiety, can affect the immune system by disrupting the production of white blood cells that fight infections, Achuthan said. "Sustained release of cortisol would therefore lead to an increased chance of infection," he said.

Breathing problems and dizziness

Rapid, shallow breathing and dizziness are common symptoms of anxiety, said Angel Enrique, a clinical psychologist at SilverCloud telehealth company.

"We feel anxiety when we expect or anticipate that something bad may happen and the body reacts to help us deal with an intense or stressful situation," he told Live Science. "This produces a fight or flight response. The body will respond by increasing our breathing so that our lungs move more oxygen through [it] in case we need to escape." However, this can make people feel short of breath, which might trigger more anxiety or panic, Enrique said.

An increased breathing pace may also lead to dizziness. "When we are anxious, we start to take in quick and deep breaths," Enrique said. "This leads to a reduction of levels of carbon dioxide in your blood causing nausea, light-headedness or tingling in [the] hands or feet."

This article is for informational purposes only and is not meant to offer medical advice.

Additional resources:

More information on anxiety disorders, from NIMH.What is Anxiety? From Anxiety.orgTips for dealing with anxiety, from ADAA.