context: Doctors still don't understand what causes multiple sclerosis. But ongoing research shows that from your genes, to where you live, to the air you breathe, there are many factors in play. MS is an autoimmune condition. Doctors don't know why, but something tells your immune system to attack your body. With MS, the focus is on myelin, a fatty substance that covers the nerve fibers in your brain and spinal cord. Its job is to protect them like the plastic that wraps around the wires in your phone charger. When myelin is messed up, your nerves can't send messages back and forth the way they should. Without their protective coating, your nerves can get damaged, too. You might be more likely to get MS if you have another autoimmune condition like inflammatory bowel disease, thyroid disease, or type 1 diabetes. MS is more likely to affect people who live in certain places and belong to specific ethnic groups. It's especially common in cooler climates like Scotland, Scandinavia, and throughout northern Europe -- places that are farther from the equator. People who live close to the equator are least likely to get it. In the U. S., it affects white people more than other racial groups. If you move from a place where MS is rare to a place where it's common before you're a teenager, you'll also be more likely to get it. This suggests that something about the place you live before puberty raises your odds of getting MS. It could be the amount of sunlight in a day. There's evidence that vitamin D, which your body makes when it's exposed to sunlight, helps protect you from immune-related diseases. Are you a smoker? Then you're also more likely to get MS. And you'll probably have a worse case that progresses faster than cases for nonsmokers. Quitting can slow the disease down, though, whether you do it before or after you're diagnosed. If you smoke and you have clinically isolated syndrome -- a first instance of MS symptoms that lasts for about 24 hours -- you have a greater chance of a second episode and an MS diagnosis. No. You don't get it from your parents. But the risk factors could be in your genes. If your parents or siblings have it, you're far more likely to get it, too. Researchers believe there's more than one gene that boosts your odds of getting MS. Some think you're born with something in your genes that makes you more likely to react to triggers in the world around you. Once you're exposed to it, your immune system responds. New ways to identify genes may help answer questions about the role genetics plays in MS. There's growing proof that hormones, including sex hormones, can affect and be affected by your immune system. For example, estrogen and progesterone, two important female sex hormones, may suppress your immune system. When these hormone levels are higher during pregnancy, women with MS tend to have less disease activity. Testosterone, the primary male hormone, may also suppress the immune response. Men's higher levels of testosterone may partly account for the fact that more than twice as many women as men have MS. Some studies have shown that two viruses from the herpes family might be linked to MS triggers. Almost all people who have the disease have proteins in their spinal fluid also found in people with a nervous system disease caused by a virus. But doctors aren't sure if the virus was there before the MS, or if it caused MS, or it just happened along with it. Yes. MS can happen at any age, but most people are diagnosed between 15 and 60. At one point, people believed each of these might cause MS. But years of research have found no links: Allergies Artificial sweeteners Exposure to heavy metals Pets Physical trauma