Cetacean skin health serves as an important indicator of individual, population, and ecosystem health. While skin lesions in toothed whales are well-documented, investigations in baleen whales remain limited. A novel skin lesion was first identified in the C1 humpback whale breeding stock off East Africa in 2013, representing the only published record to date.¹ Here, we investigated the same lesion in migrating humpback whales (E1 breeding stock) off Southeast Queensland (SEQ), Australia to determine lesion prevalence, demographic risk factors, and temporal patterns. Using photographic data from 1508 individually identified whales spanning 1994-2025, we found 50.8% presented with the lesion at least once, with prevalence increasing significantly from 39% to 48% over the study period. Susceptibility was highest in females (52%) and calves (67%). Maternal status was a critical risk factor, with lactating females showing 2.3 times higher lesion prevalence than non-lactating females and markedly higher severity. Longitudinal tracking revealed 75% of affected individuals showed chronic or maintained lesion presence, with only 20.6% achieving sustained recovery. These findings represent the first comprehensive assessment of this lesion in Australian waters, revealing concerning trends that may threaten this population's ongoing recovery and highlight an emerging health challenge requiring further investigation.