Cultural heritage serves as a repository of a place’s history and identity, integral to its landscape and central to all three sustainability goals. However, managing and protecting cultural heritage through regulatory planning often proves inadequate. This particularly applies to islands where infrastructure development pressures and urban sprawl lead to significant changes. This study quantifies the impact of uncontrolled built-up area dispersion on islands’ cultural heritage, focusing on the Southern Aegean region. By identifying and delineating the boundaries of archaeological areas and historic sites, we assess pressures through the mapping and quantitative analysis of built-up areas derived from the Global Monitoring for Environment and Security (GMES) program. The results reveal spatial relations and potential conflicts, underscoring the insufficient protection of cultural heritage due to inadequate management and ineffective planning tools. Specifically, on islands like Mykonos and Naxos, over 80% of their archaeological areas are impacted by urban sprawl. Additionally, this study finds that six islands (Antiparos, Irakleia, Kea, Mykonos, Paros and Patmos) have over 60% of their built-up areas in exurban regions, exacerbating pressures on heritage sites. These findings highlight the need for an integrated spatial planning system that incorporates landscape and cultural heritage assets into strategic planning regulations, ensuring the preservation of these essential resources amidst ongoing development pressures.