Asthma affects 1 in 5 Australian females and costs the healthcare system >$1.3b annually.1,2 Research indicates that older females living with obesity are a population of significant risk for developing asthma and having worsened asthma outcomes.3-5 Post-puberty, there is a shift from asthma being a male-dominated to a female-dominated condition, with different stages of the menstrual cycle coinciding with asthma outcomes.6 The combined oral contraceptive pill (OCP), which removes hormonal fluctuations, has been suggested to alter glucose metabolism and asthma outcomes.7 Obesity and dysregulated metabolism are also associated with worsened asthma. Given the significant sex hormone fluctuations that coincide with puberty, the menstrual cycle and menopause, sex hormones may be a contributing factor to the disproportionate impact of asthma in females.8 We hypothesise that female sex hormones influence asthma control and severity in females living with asthma and obesity, and that this is due to hormonally-induced alterations in glucose metabolism, which influences inflammation. Pre-menopausal females not using any hormonal contraception (BMI<30kg/m2 n=25, BMI≥30kg/m2 n=25) will be recruited to a longitudinal study with visits during the estrogen peak, progesterone peak and when both hormones are low. As part of a cross-sectional study, data from the longitudinal study will be compared with pre-menopausal females using the OCP (BMI<30kg/m2 n=25, BMI≥30kg/m2 n=25), and post-menopausal females not using any hormonal preparations (BMI<30kg/m2 n=25, BMI≥30kg/m2 n=25). Participants will complete lung function assessments, questionnaires and a total body composition and bone density scan. Whole blood will be collected, metabolic parameters will be quantified, and immune cells will be isolated and treated with stimuli relevant to asthma exacerbations and metabolic inhibitors. The findings of this study will establish how sex hormones, the menstrual cycle, menopause and obesity affect glucose metabolism in females with asthma, and how this influences asthma outcomes and inflammation.