Scientists have found that changes in hormone levels during the menstrual cycle can affect a woman’s stress response and immune system function. In addition, research has shown that [women with immune system disorders](http://www.webmd.com/a-to-z-guides/autoimmune-diseases) (like allergies, asthma, and lupus) may experience an increase in symptoms during the luteal phase (21 – 23rd days) of their cycle.