Experts don’t know why the immune systems attacks the thyroid like it does – could it be a virus or bacterium, or a genetic flaw? Some people are more at risk of Hashimoto’s disease than others, according to experts, which is due to their genes. Hashimoto’s disease tends to cluster in families. A 1967 paper by Hall and Stanbury published in the Journal of Clinical and Experimental Immunology noted thyroid abnormalities with clinical outcomes were observed in 33 percent of offspring of patients with Hashimoto disease or Graves' Disease.

Scientists are still looking to isolate the particular gene or genes responsible. Sex hormones may also play a part – women are more likely to get Hashimoto’s disease than men and sex hormones may explain this statistic. Pregnancy affects the thyroid gland and some women have problems with their thyroid after having a baby. Radiation exposure has been demonstrated to cause autoimmune thyroid diseases.