Why Autoimmune Diseases Disproportionately Affect Women

When you’re exposed to a cold virus or a stomach bug, your immune system powers up, battles the infection, and then retreats. But what if that response is misguided, and then fights you instead?

That’s what happens in autoimmune diseases, a group of conditions including rheumatoid arthritis, lupus, Hashimoto’s thyroiditis, and many more. Something triggers the immune system, designed to recognize foreign cells and fight them off, to attack your own cells. This causes a wide range of symptoms from fever and aches to skin and digestive issues.

There are more than 80 different autoimmune diseases that affect more than 24 million people in the U.S. While researchers don’t know exactly what causes autoimmune disease , many experts believe they’re triggered by infections; the immune system revs up to handle the virus or bacteria and becomes overactive. Genetics, lifestyle factors like obesity and smoking, and certain medications can also be risk factors. And, for reasons scientists don’t totally understand, women represent more than 75 percent of cases .

There are several theories about why women are more prone to autoimmune diseases. One group of theories relate to hormones, specifically the differing ratios of estrogen and testosterone that men and women have, as well as the role of changing hormones throughout life. For example, a 2018 study in Nature Communications found that testosterone suppresses a protein that makes B cells, a type of immune cell that can release autoimmune antibodies, stronger. Since women have less testosterone, those B cells are able to proliferate and release harmful antibodies. Other research finds that the immune system and hormone levels are in a delicate balance; when hormones shift during puberty, pregnancy, and menopause, the balance may be disrupted, and women become vulnerable to autoimmune diseases. Pregnancy itself may also make women more susceptible, says Dawn Jacobson, M.D., a doctor formerly with Parsley Health. When a woman is pregnant, the fetus’s cells get into her circulatory system. They can be stored in tissues, such as the bone marrow, for over a decade after the pregnancy. “One theory is that the immune system recognizes these fetal cells as foreign and creates an autoimmune response,” she says.