Yes, multiple sclerosis is on the rise. Global incidence increased by nearly 50% between 1990 and 2021, and the trend shows no signs of reversing. In the United States alone, almost 1 million people are now living with an MS diagnosis, more than twice the estimate from previous studies. Some of this increase reflects better detection, but a genuine rise in cases is happening as well, driven by environmental and lifestyle shifts that researchers are only beginning to untangle.
How Much MS Has Increased Worldwide
A 2025 analysis published in Frontiers in Neurology, drawing on Global Burden of Disease data, found that new MS cases among adults aged 20 to 54 rose by 49.48% globally between 1990 and 2021. That translates to roughly 52,000 new cases per year worldwide, up from about 35,000 in 1990.
The increase is not evenly distributed. Some regions saw dramatic spikes: western Sub-Saharan Africa experienced a 226% increase in new cases, Andean Latin America rose by 195%, and the North Africa/Middle East region climbed by 174%. Meanwhile, high-income North America saw a comparatively modest 16% rise, and Western Europe grew by about 27%. These differences likely reflect a combination of population growth, improving diagnostic access in lower-income countries, and shifting environmental exposures.
Pediatric-onset MS is rising too. While the total numbers remain small (roughly 1,900 new cases globally in 2021), the trend line has been consistently climbing for decades. This matters because earlier onset typically means a longer disease course and greater lifetime disability burden.
Better Detection Explains Part of the Rise
Not every new diagnosis represents a truly new case. Diagnostic criteria have gotten more sensitive over time, and MRI technology has become far more widely available. The 2017 revision of the McDonald diagnostic criteria, the standard framework neurologists use to confirm MS, shortened the median time from first symptoms to diagnosis from over four years to about three months. Its sensitivity jumped from 66% to 83% compared to the previous version. That means people who would have gone undiagnosed for years, or been missed entirely, are now being identified earlier.
This detection effect is especially strong in regions that previously had limited access to MRI machines and neurologists. A country that installs its first MRI centers will naturally see a spike in MS diagnoses, not because the disease suddenly appeared, but because it was always there and is now being found. This partly explains the enormous percentage increases in parts of Africa, Latin America, and South Asia.
Still, detection improvements alone cannot account for the full picture. Researchers tracking populations with consistent diagnostic access over time, particularly in Scandinavia and other parts of Northern Europe, have documented genuine increases in incidence. The rise is real, even after accounting for better tools.
Why Cases Are Genuinely Increasing
Several environmental and biological factors are converging to push MS rates upward.
Vitamin D Deficiency
Low vitamin D levels are one of the strongest modifiable risk factors for MS. A large genetic study published in PLOS Medicine found that each meaningful decrease in blood vitamin D levels doubled the odds of developing MS. Modern lifestyles involve far more time indoors than previous generations, and widespread sunscreen use, while important for skin cancer prevention, further reduces vitamin D production. The result is that populations across the world have lower vitamin D levels than they did decades ago, and this appears to be contributing to rising MS rates.
Epstein-Barr Virus
Epstein-Barr virus (EBV), the virus that causes mono, appears to be a necessary precondition for MS. More than 99% of people with MS have been infected with EBV, compared to 90 to 95% of the general population. A landmark study tracking millions of military personnel found that EBV infection increased the risk of developing MS by 32-fold, with symptoms typically appearing about five years later. People who experienced symptomatic mono had more than twice the risk compared to those with silent EBV infections. Since nearly everyone eventually catches EBV, the virus alone doesn’t explain the rise. But it sets the stage, and other factors determine who among the infected actually develops MS.
The Hygiene Hypothesis
One theory gaining traction is that modern sanitation, while obviously beneficial overall, has altered our immune development in ways that increase autoimmune risk. The idea is that growing up in extremely clean environments deprives the immune system of the microbial exposure it needs to learn proper self-regulation. Research has found that people with MS have lower circulating levels of certain microbial products from their gut bacteria, suggesting their microbiome isn’t providing the immune-calming signals that help prevent the body from attacking its own tissues. As sanitation improves worldwide, this could be contributing to rising autoimmune diseases broadly, MS included.
Women Are Increasingly Affected
One of the most striking trends is how the gender gap has widened. In the 1940s, the National MS Society reported that MS affected men and women equally. By the 1980s, the ratio had shifted to 2 women for every 1 man. Today, it stands at roughly 3 to 1 and continues to grow. This widening gap points strongly toward environmental or hormonal factors, since genetic susceptibility between sexes wouldn’t change this quickly. Researchers are investigating the interplay between female sex hormones, reproductive patterns, and immune function, but no single explanation has emerged. The fact that the ratio is shifting so rapidly, over just a few decades, suggests that whatever is driving the overall rise in MS is hitting women disproportionately hard.
The Latitude Pattern Is Fading
For decades, MS was considered a disease of higher latitudes. The farther you lived from the equator, the more common it was, a pattern that neatly aligned with reduced sun exposure and lower vitamin D levels. That pattern is now breaking down. A meta-analysis found that the expected north-south gradient of MS incidence could not be confirmed in Europe or North America, even when looking only at data from before 1980. MS is spreading into regions where it was once rare, including parts of the Middle East, Latin America, and Sub-Saharan Africa. The old rule that MS is a “Northern European disease” no longer holds. On the southern hemisphere the gradient still appears to exist, but globally, MS is becoming a more universal condition.
What This Means Going Forward
The rise in MS is not a single story with a single cause. It is a combination of genuinely increasing incidence, better and earlier diagnosis, and expanding medical infrastructure in parts of the world where MS previously went unrecognized. The environmental factors most strongly linked to the increase, vitamin D deficiency, changing microbial exposures, and possibly obesity, are all trends that show little sign of reversing on a population level. The 2025 Global Burden of Disease projections extend to 2035 and anticipate continued growth, particularly in low- and middle-income countries where diagnostic capacity is still expanding and lifestyle factors are shifting rapidly toward Western patterns.
For individuals, the practical takeaway is that MS awareness matters beyond the populations traditionally considered at risk. Maintaining adequate vitamin D levels, recognizing early symptoms like unexplained numbness, vision changes, or unusual fatigue, and understanding that MS can appear in populations and age groups where it was once considered uncommon are all relevant in a world where this disease is becoming more widespread.