The number of people who have multiple sclerosis (MS) increases the farther away they are from the equator.

In areas near the equator, MS occurs in 1 in 100,000 people. In areas farther from the equator—such as northern Europe and northern North America—MS occurs in around 30 to 80 of every 100,000 people.¹ When moving south of the equator, the number of people with MS is less dramatic, but the same trend is seen.

Some evidence suggests that people who move from a high-risk to a low-risk area before the age of 15 reduce their chances of developing MS. However, the same is true in reverse—in those who move from a low-risk area to a high-risk area before the age of 15, the risk of getting MS increases.¹ Those older than 15 when they move to a new area retain the risk associated with their old area.

Most experts agree that this unusual relationship between geographic location and MS suggests that an environmental factor is partly responsible for causing the disease.