Abstract Background/Aims Despite being commonly reported by patients, the occurrence of episodic ‘flare’ and factors affecting it have not previously been studied in hand osteoarthritis. We investigated the associations between short-term fluctuations in hand pain and clinical/constitutional factors (including female hormonal and reproductive exposures) in individuals with hand osteoarthritis. Methods HOPE-Cohort was a remote, 6-month prospective study. Males and females were recruited UK-wide from the community, primary and secondary care, with clinically-diagnosed hand osteoarthritis (≥ 2 joints involved), who were not in flare at baseline. Baseline data collected included age, sex, BMI; clinical involvement of hand joints; psychological status (including pain self-efficacy, anxiety); and in females, age of menopause, history of oophorectomy/hysterectomy, Hormone Replacement Therapy (HRT) use and menopausal symptoms score. Hand pain severity was recorded daily for 6-months by participant smartphone (REDCap weblink within daily SMS) using a 0-10 numerical rating scale (NRS). Participants self-reported onset of flare, triggering an additional flare survey to further characterise flare episodes. These data sources yielded the following outcomes: (i) average hand pain severity (NRS) at baseline; (ii) hand pain variability across 6-months, by intra-individual standard deviation (IISD) of daily pain NRS; and (iii) count of participant-reported flares. In sex-stratified analyses, associations between baseline variables and these outcomes were assessed by univariable and multivariable regression (linear or Poisson, depending on the outcome) using STATA IC 18.0. Results 132 participants (median age 64) were recruited, of whom 121 (94%) provided pain scores on ≥ 90 of 180 possible days. 114 (86%) were females of whom 87% were post-menopausal, with history of hysterectomy and oophorectomy in 18% and 9% respectively. 87% (105/121) experienced ≥1 hand osteoarthritis flare over 6-months. Amongst females, median flare frequency was 2.5 (IQR 1,4, range 0,11). During a flare, daily pain NRS increased by median 1.5 (IQR 0.9,2.5). Median flare duration was 5 days. In females, adverse scores on all psychological measures, prior hysterectomy and higher menopausal symptoms score were all associated with greater baseline hand pain severity. Greater baseline pain NRS was associated with greater within-participant pain variability (increase in IISD β 0.09 [95%CI:0.06,0.13]; R2=0.22). After baseline pain adjustment, lower pain self-efficacy, higher BMI and absence of current HRT were all associated with greater hand pain variability. Greater baseline pain was also associated with greater frequency of participant-reported flares, IRR 1.17 (95%CI:1.07,1.27). After adjusting for baseline hand pain, several factors remained associated with increased flare frequency, including history of hysterectomy, oophorectomy, plus menopause factors (lower age; increasing interval since). Conclusion This study provides novel data on the varying pain experience in hand osteoarthritis and evidence for flare episodes being a recognisable feature for many. In post-menopausal females, underlying hormonal factors may be relevant in explaining the course and severity of hand pain. Disclosure M. Gulati: Grants/research support; MG has a Clinical Research Fellowship from Versus Arthritis [Grant number 21604]. MG is in receipt of a Clarendon Scholarship [Oxford University Press]. G. Brewer: None. T.A. Perry: None. B. Marsden: None. M. Schlussel: None. N.K. Arden: None. G.S. Collins: None. K. Vincent: Consultancies; K.V. has had consultancy fees paid to her institution from Gedeon Richter, Reckitts, AbbVie, Bayer Healthcare and Gesynta. Honoraria; K.V. has received honoraria for lectures. T.L. Vincent: Consultancies; T.V. is a current advisory board member for Zoetis. Grants/research support; T.V. has received research funding in the past 5 years from Pfizer, UCB, Novartis, Fidia, Biosplice. A. Silman: None. F.E. Watt: Consultancies; F.W. has received consultancy fees from Pfizer in the past 5 years. Grants/research support; FW has a fellowship from UK Research & Innovation (UKRI) [Grant numbers MR/S016538/1, MR/S016538/2 and MR/Y003470/1).