The rapid expansion of informal settlements and slums in southwestern Nigeria, particularly along the Lagos-Ogun-Oyo corridor, underscores the critical challenges posed by rapid urbanisation and population growth in this major economic hub of West Africa. This corridor, home to key infrastructure, industries, and economic activities, has seen a significant rise in unplanned communities due to its economic opportunities. In particular, Ogun and Oyo states, both sharing borders with Lagos, have become hotspots of these communities, characterised by inadequate housing, poor sanitation, unsafe drinking water, and heightened vulnerability to climate-related hazards. In this viewpoint, we examine the health and environmental challenges faced by residents in these informal settlements, including respiratory illnesses, waterborne diseases, and climate-related health risks exacerbated by poor air quality and extreme heat. Despite various research efforts, policy reforms, and programmatic interventions, challenges such as limited funding, inadequate enforcement, and a lack of coordination among stakeholders persist. We propose a holistic, multi-sectoral approach that could improve living standards and health outcomes through community empowerment, participatory urban planning, microfinance initiatives, and climate resilience programmes. We note that this requires collaborative efforts from government, nongovernmental organisations, and local residents to create sustainable and resilient urban environments.