During the 1920s and 1930s a variety of forces came into play to weave sunlight, as a giver of health, into the fabric of social worlds. Both the People’s League and the New Health Society played an active role in public health campaigns concerning the benefits of sunlight. Yet these organisations were not principally concerned with sunlight itself. Instead they sought to frame the health benefits of sunlight exposure in order to stabilise a specific social figuration as part of the broader social hygiene movement. However, in the early 1920s an organisation appeared that sought to actively promote the action of the sun’s rays as being a health benefit in their own right and to materially ‘domesticate’ the sun’s rays: namely Caleb Saleeby’s Sunlight League founded in 1924. The League campaigned, both directly and via its journal (Sunlight), for a variety of causes such as, mixed sunbathing, open air schools and the general health benefits of sunlight. But foremost amongst these was the cause of smoke abetment. Smoke pollution was seen as a key threat to the health of urban populations because it deprived the climate of the ‘health giving’ effects of ultra-violet light. Saleeby came to refer to the combination of smoke abatement policies together with the prophylactic application of the sun’s rays as helio-hygiene. In this paper I will examine the promotion of a sunlit climate in this period in order to chart the emergence of a nexus made up of bodies, sunlight and social worlds. I have termed this assemblage the heliosis – to capture the idea of an interactive stabilization between the various knotted couplings of the human body in a sunlit climate.