Causes of MS
No one knows for sure why people get MS. It's likely to be due to a mix of genes, something in your environment and some lifestyle factors.
Genes and family history
MS is not directly inherited from parent to child. There's no single gene that causes it. Over 100 genes might affect your chances of getting MS. But genes are only part of the story.
MS can happen more than once in a family, but it's much more likely this will not happen. There's only about a 1.5% chance of a child developing MS when their mother or father has it (that means around one in 67 get it). There's only around a 2.7% chance that you'll get MS if your brother or sister has it (around one in 37 get it). In 2014 a very large study found that MS may be even less likely to be passed on than these figures suggest.
MS is less common in hot, sunny tropical countries near the equator. More people have MS in places like Britain, and that's true no matter what your ethnic background is. Other countries where MS is more common include Canada, the US, Scandinavia, southern Australia and New Zealand.
There's evidence that some viruses, and maybe bacteria, can help trigger MS.
A common virus called Epstein Barr virus (it causes glandular fever) has been linked to MS. Most people have had this virus but they never get MS. This shows that, like genes, infections might play a role but they aren't the whole story.
There's more and more evidence that low levels of vitamin D, especially before you become an adult, could be a factor in why some people get MS.
Our skin makes most of our vitamin D when we're out in the sun. We also get some from food like oily fish, eggs, spreads and breakfast cereals with added vitamin D in them. You can also get extra vitamin D from supplements (but too much can be harmful).
A blood test can show if your levels of vitamin D are low.
Read more about vitamin D in our research section.
Studies show you're more likely to get MS if you smoke. It might be because the chemicals in cigarette smoke affect your immune system. Passive smoking - breathing in other people's smoke - is also linked to a higher risk of getting MS.
If you have relapsing MS and you stop smoking it can slow down how fast your MS changes to secondary progressive MS.
Studies show that getting MS could be linked to being very overweight (obese), especially when you were a child or young adult. This might be because obese people are often low in vitamin D. Obesity can also make your immune system overactive and cause inflammation in your body. There may be other reasons we don't understand yet.
Of course, not all people who are very overweight get MS, and having MS doesn't mean you are or were obese. But if your risk of getting MS is on your mind, perhaps because a close relative has it, then your weight is a risk factor you can change.