Why Multiple Sclerosis Affects More Women Than Men

Medically Reviewed by Carol DerSarkissian, MD on March 17, 2024
2 min read

Women with MS outnumber men with the condition by nearly 4 to 1. And this gender gap has only widened in the last 50 years. Experts don’t have a clear explanation for the cause of MS in anyone, much less in women specifically. But they have a few theories that might explain the sex differences in MS rates.

Women’s immune systems work differently from men’s. Specifically, women are more likely to develop autoimmune diseases. In fact, nearly 7 in 10 people with autoimmune diseases are women.

The difference might lie in an immune system protein called interleukin-33 (IL-33). It helps cells within the immune system communicate with each other. This is how they work together to fight off infection.

Current research explores what role IL-33 might play in immune system responses in men and women.

Early studies show that men make more IL-33 than women when they face infections. This may explain why women are more likely to have an autoimmune response than men are.

Men tend to get more nerve damage with MS than women do. Researchers think this may have to do with estrogen levels. Women’s bodies produce more estrogen than men’s. This leads researchers to ask whether estrogen may protect nerves in some way.

One reason that more women develop MS than men could have to do with reproductive hormones. Before puberty hits, boys and girls tend to get MS at about the same rate. But as boys and girls move into adolescence and adulthood, when the male and female bodies make different hormones, women begin to get MS at higher rates than men. This difference pushes researchers to consider a possible link between male and female sex hormones and MS. 

Mutations in certain genes called MHC genes may raise the risk for MS. Some research shows that women with MS are more likely to have relevant changes in these genes than men. Daughters are also more likely than sons to inherit those gene changes from their mothers.

But a gene alone likely doesn’t cause MS. Researchers think that other factors in your life, such as diet, smoking, stress, and the amount of sunlight you get, influence how these MS-related genes behave.

Obesity, especially in the form of belly fat, can cause inflammation in your body. And inflammation plays a role in MS. Obesity-related inflammation may arise more often in women than in men. That’s because women tend to carry more body fat than men do, and they are more likely to become obese. Scientists think the rising numbers of women with MS may relate to this higher percentage of body fat.