Multiple sclerosis (MS) is one of the most widespread disabling neurological condition in young adults across the world, affecting more than 2.3 million people. Although MS is not contagious or directly inherited, scientists have identified factors affecting the distribution of MS that may help determine what causes the disease. These factors include age, sex, race, genetics, and geographical location.

The median estimated prevalence of MS is 30 per 100,000 people (prevalence is the number of people with a condition, measured per 100,000) and the median estimated incidence of MS is 2.5 per 100,000 (incidence is the number of new cases of a condition within a period of time, usually one year).

Although MS can develop at any age, most people are diagnosed between 20 and 50 years of age, with an average age of onset of 29.2.

MS is two to three times more common in women than in men, which suggests that hormones may have a meaningful role as a susceptibility factor.

Research showed that MS is more common in areas farthest from the equator. White people, especially those of Northern European descent, are at highest risk of developing MS. People of native American, Asian or African descent have the lowest risk of developing MS.

Some ethnic groups have a significantly lower prevalence of MS even if the country they live in has a greater rate. The Sami or Lapps of northern Scandinavia and the Inuits in Canada have very low rates of MS. This is also true for the Maoris in New Zealand, the Australian Aborigines, and the Hutterites. The link between ethnicity and the risk of developing MS is not understood.
