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About 60 percent of adults have a chronic disease, according to the Centers for Disease Control and Prevention. But, not all illnesses can be measured or come with visible signs or symptoms. In those cases, the condition might be considered an invisible illness.
An invisible illness is an umbrella term for any medical condition that doesn’t present with “overt symptoms, clear diagnostic markers, or definitive symptoms,” explains Evelyn Darius, MD, a physician with virtual health platform PlushCare.
“In other words, people with invisible illness often appear ‘normal’ to the observer,” she says. “They typically experience chronic pain or discomfort that cannot be explained by other illnesses.”
Because of that, some people with an invisible illness are sometimes not taken seriously when they seek treatment, Darius adds.
The tricky part of diagnosing an invisible illness is that physicians often lack a “best tool” to measure or assess the cases in a quantifiable way, says Robert Bolash, MD, a pain management specialist at Cleveland Clinic. For example, pain doesn’t show up on a CT scan or MRI.
“Because we are unable to easily measure pain in routine clinical practice, a number of pain diagnoses may be considered invisible,” he explains.
What types of conditions fall into the “invisible” category? Here a look at
12 Invisible Illnesses
1. Axial spondyloarthritis
Axial spondyloarthritis is a type of inflammatory arthritis that causes lower back pain and other issues, according to the Spondylitis Association of America. It’s a broad category that includes people with and without damage or fusing of the joints linking the lowest part of the spine to the pelvis.
“Patients with substantial arthritic pain from the spine can have normal blood work and normal imaging, yet exhibit significant pain arising from these small joints,” Bolash says. “Their pain is real, but our tools just haven’t quite caught up to best assess it.”
2. Multiple sclerosis
Multiple sclerosis is a chronic autoimmune disease of the central nervous system that can have visible and invisible symptoms. There’s no cure for MS, and it will eventually lead to some level of disability for most people, says Lori Travis, MD, a board-certified neurologist at Phoenix Neurological Associates.
“Signs and symptoms of MS, including those not visible to the eye—such as fatigue, pain and blurred vision—vary widely from person to person and change over the course of the disease, temporarily disappearing or progressively worsening,” she explains. Memory loss, weakness, prickly or tingling sensations, and balance problems are other symptoms that may be invisible.
3. Fibromyalgia
This chronic illness causes muscle and joint pain, and fatigue that may come and go, according to Cleveland Clinic. It may also cause digestive problems, anxiety and memory problems. Fibromyalgia has no known cause, and there isn’t a cure or an exact way to measure someone’s pain due to the condition.
“People have pain, but maybe they look healthy and well put together on the outside,” says Peter Abaci, MD, pain expert and author of Take Charge of Your Chronic Pain. “Yet, they don’t feel well on the inside.”
4. Crohn’s disease
Crohn’s disease is an inflammatory bowel disease causing swelling and irritation in the digestive tract. Symptoms include abdominal pain, chronic diarrhea, weight loss and fever—and, they can be severe sometimes, and mild or nonexistent at other times.
Most symptoms aren’t visible. “While someone may look fine, their intestines may be inflamed and ulcerated, they may be in excruciating pain, and their immune system is essentially attacking itself,” says the Crohn’s & Colitis Foundation.
Related: What is IBS?
5. Irritable bowel disease
Gastrointestinal symptoms, such as indigestion, constipation, abdominal pain and diarrhea, are common with invisible illnesses, Darius says. These are also common symptoms of irritable bowel syndrome (IBS), a gastrointestinal disorder.
People with IBS may have flare-ups, where symptoms are more severe than at other times. They may also experience embarrassment and stress with having the condition, which usually isn’t outwardly visible.
6. Rheumatoid arthritis
Pain, joint stiffness and fatigue are symptoms of rheumatoid arthritis that aren’t always apparent to outsiders. According to Cleveland Clinic, rheumatoid arthritis is an autoimmune disease, where the body’s immune system overreacts, causing pain and other problems. It differs from other kinds of arthritis because it usually affects joints on both sides of the body, such as both hands or both knees.
Related: Psoriatic Arthritis vs. Rheumatoid Arthritis Explained
7. Sjogren’s syndrome
Some medical experts refer to Sjogren’s syndrome as the “invisible autoimmune disease.” It attacks tear and saliva-producing glands causing dry mouth and eyes, as well as pain and fatigue. Some people with the condition experience dry, gritty eyes or an abnormal sense of taste. Sjogren’s syndrome can develop on its own or along with other conditions, like rheumatoid arthritis or lupus.
8. Cancer
Cancer can develop and spread slowly. But, it depends on the type of cancer and individual patient. For example, some breast cancers are slower moving.
Because of the speed of how many cancers progress in the body, Brian LaMoreaux, MD, a rheumatologist and senior medical director at Horizon Therapeutics, says it can be an invisible illness, “When something harmful is growing inside the body, but there aren’t other clear external manifestations yet.”
9. Depression and anxiety
Many mental health conditions, including depression and anxiety, are invisible illnesses since people often don’t display externally visible symptoms, says Jeffrey Stark, MD, head of immunology medical affairs at pharmaceutical company UCB.
And, living with a chronic condition, especially an invisible illness, can make someone feel “unseen and isolated,” which Stark says can affect their quality of life. “Those living with invisible illnesses unfortunately not only deal with their chronic conditions, but can also be victims of judgment and criticism because others believe they look fine on the outside, and therefore assume they must be ‘making up’ their suffering,” he adds.
Related: When to Talk to a Therapist About Anxiety
10. Diabetes
Diabetes causes a number of symptoms that aren’t always evident to anyone not dealing with the condition. These symptoms include blood sugar fluctuations, extreme thirst, fatigue, blurred vision and numbness in the fingers and toes.
Along with the physical symptoms, living with diabetes can also affect your mental health. People with diabetes are about three times as likely to experience depression, and only a fraction of these individuals seek treatment for depression, according to the CDC.
11. Lupus
The most common type of lupus, systemic lupus erythematosus, is another invisible illness, Darius says. Lupus is a chronic, autoimmune disease in which the immune system attacks its own tissues, causing widespread inflammation.
The disease affects women more than men, and it typically affects the skin, joints, heart and kidneys, according to the Lupus Foundation of America. But, lupus impacts many parts of the body, so it can cause many different symptoms. How severe the symptoms are varies from person to person, too.
12. Migraines
Migraines are one of the most common illnesses—about a quarter of U.S. households includes someone who gets migraines, according to the Migraine Research Foundation. Women more often experience migraines than men. Why so many people get migraines isn’t widely understood, and there’s no test to specifically diagnose the condition, Abaci says. And, most people who get migraines don’t seek medical help.
Headaches, pain in the neck, dizziness and sensitivity to light and sound are common with migraines, but the severity varies. People who get migraines also often struggle to get enough sleep and experience depression and anxiety.
How to know if you have an invisible illness
Any illness, whether it’s considered visible or invisible, can present in many different ways. If you have any symptoms that aren’t resolving on their own or are interfering with your life, visit your doctor, LaMoreaux says. Fever, chills, fatigue, aches or just not feeling well could signal inflammation in the body.
“Even though there is nothing obvious on the outside, it does not mean everything is fine,” he explains. “Your doctor can provide you with a detailed evaluation, exam, and get appropriate testing to uncover what is beyond the obvious.”
Taking your medical history and performing a physical exam is always necessary, because there may not be a specific test to measure each illness, Bolash says.
“Doctors act as sleuths to assemble the challenges you’re having into one unifying diagnosis,” he says.