What Is Multiple Sclerosis?

This informational guide, part of POPSUGAR's Condition Center, lays out the realities of this health concern: what it is, what it can look like, and strategies that medical experts say are proven to help. You should always consult your doctor regarding matters pertaining to your health and before starting any course of medical treatment.

Multiple sclerosis impacts an estimated 2.8 million people worldwide, according to research from the Atlas of MS. It's the most common disabling neurological disease in young adults and symptoms usually start between the ages of 20 to 40 years, creating a significant impact on a patient's adulthood, per the National Institute of Neurological Disorders and Stroke (NINDS).

Multiple sclerosis (MS) has been in the news more recently as celebrities like Christina Applegate and Selma Blair have continued to open up about their diagnoses. But not everyone understands the disease and how complex it can be. Here's what you need to know about MS.

Multiple sclerosis, or MS, is characterized as an autoimmune condition. It happens when the immune system, which typically protects you from viruses, bacteria, and other pathogens, mistakenly attacks the myelin in the central nervous system, according to NINDS. Myelin, in case you're not familiar with it, is a substance that makes a protective covering that coats nerve fibers.

These attacks by the immune system "cause injury to the central nervous system — the brain, the spinal cord, and the optic nerve to the eye," says Nicholas Lannen, MD, a neurologist specializing in neuroimmunology at Corewell Health in Grand Rapids, MI. "The brain is almost always involved," he adds.

Multiple sclerosis is usually a progressive illness, which means it gets worse over time. "Each attack against the brain causes a patch to swell and then scar," explains Amit Sachdev, MD, MS, medical director in the department of neurology at Michigan State University. "Patches that are swollen don't work right, so people lose something during the attack like feeling or movement. When the swelling goes down, the patch can recover, but a scarred area is left behind. Scars never work quite right again."

Symptoms can vary depending on which part of the central nervous system is injured, Dr. Lannen says. "For example, some people with a significant amount of brain injury may develop issues pertaining to cognition and how quickly they can process thoughts," he says. "If the optic nerve is injured, patients often experience visual loss. Spinal cord injury can be particularly debilitating and cause a wide array of issues such as weakened motor skills, numbness, or issues with bowel or bladder function." Other symptoms can include fatigue, muscle weakness, tingling or numbness, balance issues, dizziness, and mood changes, NINDS says.

There are also different types of MS, NINDS explains. Those include:

Much of MS is still a mystery. "We don't know why MS happens, but we do know that MS is a disease where the immune system attacks the brain," Dr. Sachdev says. Lannen agrees. "MS is a complicated disease," he says. "We believe it is triggered by particular risk factors in genetically susceptible people [but] there is not a single gene that causes MS. There are likely thousands of genes that can increase or decrease the person's risk of MS."

Environmental risk factors can also increase a person's risk of developing multiple sclerosis, including infections, vitamin D levels, body mass index, smoking status, and where someone grew up, Dr. Lannen says.

There is a theory that the Epstein Barr virus may play a role in the development of multiple sclerosis, but it's unproven at this time. "Studies have shown that exposure to Epstein Barr virus, which also causes mononucleosis, is seen in basically all people with multiple sclerosis," Dr. Lannen says. But, he points out, more than 90 percent of adults test positive for it regardless of whether they have MS, making it difficult to say this virus definitively causes MS.

As for flares of symptoms, they can be caused by a range of things. "People sometimes get increased symptom activity when the weather changes—often when it's more humid," says Barbara Giesser, MD, a neurologist and MS specialist at Pacific Neuroscience Institute in Santa Monica, CA. An illness, surgery, heat, and stress can also lead to flares, Dr. Sachdev says. "When the immune system surges in response to something else, it can attack the brain," he explains.

There are many treatment options when it comes to MS. According to the NINDS, some of the most common ones include:

Finding the right treatment usually involves a detailed conversation with a neurologist. "After I diagnose someone with multiple sclerosis, we discuss the treatment options that are available to help prevent or curtail new attacks," Dr. Lannen says. "We work together to select the drug we think is best."

Dr. Giesser says that MS treatment is "not one size fits all — it involves disease-modifying therapy, symptom management, and lifestyle modifications." Exercise, for example, is very important for people with MS to help address balance, strength, mobility, depressive symptoms, and quality of life, according to the International Journal of Environmental Research and Public Health.

Treatment will often need to change for patients over time, Dr. Sachdev says. "MS is a lifelong disease and it is unlikely that one drug will be the right fit for your whole life," he says. "We use one medicine until we need to change."