By Sandee LaMotte

CNN

(CNN) -- It's a centuries old disorder that wasn't recognized as worthy of research funding until 2005.

Its mark on the body is often invisible. Yet millions around the world suffer from it.

Its symptoms, such as fatigue, confusion, shortness of breath and joint pain, are so common that many of its victims, predominantly women, are written off by society as "lazy or crazy."

Yet inflammation can easily flare, leading to lengthy hospitalizations, even death. What is this frustrating, covert disease that can take such a toll?

Lupus, also known as systemic lupus erythematosus or SLE.

"But you don't look sick," is the most common refrain that a person with lupus will hear, said Christine Miserandino, a lupus patient and chronic disease advocate who runs a website by the same name butyoudontlooksick.com. As she often points out in her writings and speaking engagements, that well-meaning phrase can backfire.

"Many times, being pretty or not sickly looking makes it harder to validate an illness you cannot see," said Miserandino.

Lupus risks

Lupus is a chronic inflammatory condition where the body's immune system attacks its own healthy cells and tissues. Any system or organ in the body can be affected -- the skin, lungs, blood cells, heart, joints, brain or kidneys -- so lupus looks different in everyone.

Because of that, it can be hard to get a diagnosis, as doctors confuse symptoms with other diseases, or discount them entirely.

Selena Gomez and other celebrities

Actor Kristen Johnston, best known for "3rd Rock from the Sun" told her fans on Facebook that it took 17 doctors and "two fun-filled weeks in November partying at the Mayo Clinic" before she was diagnosed in 2013 with lupus myelitis. That's a rare form of the disease that attacks the spinal cord.

When pop star Selena Gomez took a break from one of her tours, she battled rumors of substance abuse before telling the media that she had lupus.

"I've been through chemotherapy. That's what my break was really about. I could've had a stroke," she told Billboard.

The willingness of other celebrities, such as Grammy award winning singer Toni Braxton, U.S. soccer team player Shannon Boxx, actor and television personality Nick Cannon, and singer-songwriter Seal, who wears the scars of discoid lupus erythematosus on his face, have helped the disease gain national attention and foster understanding of its many challenges.

Lupus causes

Lupus can attack at any age, but most commonly arrives between the ages of 15 and 44. Women, African Americans, Hispanics and Asians are more likely to be affected. There is no cure and no definitive cause.

There is a form of drug-induced lupus, caused by certain antibiotic, seizure or blood pressure medications, but it normally resolves after the drug is withdrawn. In most cases, experts believe there could be a genetic component to lupus, triggered at some point by an outside cause, such as infection, even sunlight.

Lupus symptoms

While each case of lupus is unique, there are some common symptoms. Nearly everyone with lupus will experience joint pain and inflammation, which can progress to arthritis. Chronic fatigue, unexplained fever, shortness of breath, headaches, hair loss, mouth sores and sensitivity to sunlight are typical.

A facial rash that extends across the forehead, cheeks and nose, and shaped similar to a butterfly, occurs in about half of all cases.

One of the most frustrating symptoms of lupus is frequent confusion and memory loss. Around one in five people with lupus suffer from some sort of brain fog, which happens when lupus antibodies cross the blood-brain barrier and interfere with the brain's memory center. Most attacks are mild, such as forgetting a familiar number or where you parked your car, but for some memory loss can worsen over time.

Lupus also raises the risk of pregnancy complications, infections, even cancer, so obtaining treatment for the condition is critical to living with the disease.

Lupus treatment

Typical treatments for lupus include an immunosuppressant to slow the body's attack on itself, prednisone and other types of corticosteroids to reduce inflammation, and over the counter pain relievers, such as naproxen sodium and ibuprofen to treat fever and swelling.

The first prescription treatment for lupus in over 50 years was approved in 2011 by the Food and Drug Administration. The drug, Benlysta, is a biologic, which means it was made in a living organism rather than chemically, and works by specifically targeting overactive antibodies, rather than suppressing the entire immune system. It's given intravenously, and only to those patients for whom other treatments have become ineffective.

There is some evidence that vitamin D, fish oil and DHEA (dehydroepiandrosterone) supplements can help as well. Because sunlight is a trigger, it's important that anyone with lupus wear protective clothing, sunglasses and sunscreen.

Lupus triggers

Lupus is a variable disease, characterized by periods of wellness with few symptoms, followed by an extreme "flare" of the disease, often triggered by a factor in the patient's environment. Common triggers include stress, cold, flu and infections, exhaustion, ultraviolet rays from sunlight and in some cases, florescent lights, and various medications, especially those that increase sun sensitivity.

Experts suggest avoiding flares by practicing a healthy lifestyle: eat a well-balanced diet, get plenty of sleep and exercise, and avoid as much daily stress as possible. Staying out of sunlight is also key, as is keeping a journal of symptoms to help identify flares early and get immediate medical care.