Desertification, the spread of desertlike conditions as a result of a combination of climatic fluctuations and human impacts, is a form of land degradation that occurs in and around the world's drylands. Considerable debate surrounds the speed, nature, and causes of desertification, but it undoubtedly has a series of health implications. One group of these is associated with indirect human impacts of the phenomenon, including mass migrations, poverty, food and water shortages, and conflict over land and water resources. Another group of health problems is associated with reductions in water quality, whether in terms of availability or, more importantly, in terms of salt and particulate loadings. Possibly the most pervasive health consequences of desertification are reductions in air quality caused by the buildup of dust particles in the air. Among the human health considerations associated with dust (mineral aerosol) in the atmosphere are respiratory problems, heart disease, silicosis, conjunctivitis, meningococcal meningitis, and coccidioidomycosis (Valley Fever).