Asthma is a non-communicable and non-curable lung disease that is associated with an array of environmental contaminants and chemicals. Many of these hazards are subject to regulation, or may be considered for regulation, in order to reduce exposures and prevent human health risks. However, the available information on willingness-to-pay (WTP) to avoid asthma or reduce its severity is scarce, incomplete and does not provide estimates compatible with welfare economic theory that can be used in cost-benefit analysis. This paper is part of the series of large scale willingness to pay (WTP) studies resulting from the Surveys to elicit Willingness to pay to Avoid Chemicals related negative Health Effects (SWACHE) project that intends to improve the basis for doing cost-benefit analyses of chemicals management options and environmental policies in general. The present paper offers values suitable for use in cost-benefit analyses of the WTP for reduced severity of asthma attacks in adults and children and in reduced probability of getting asthma for these two population groups, all in the context of reducing chemical exposures, and covering populations in seven OECD countries: Canada, Czech Republic, France, Poland, Sweden, the United Kingdom and the United States. The context for such WTP elicitations was a set of household products that contain fewer hazardous chemicals than what is currently available in supermarkets but are more expensive.