Houston tops the list of cities with the most damaged hair, according to an index compiled by Procter & Gamble based on consumer habits and environmental factors such as UV levels, relative humidity, precipitation, pollution and population. Close behind are New Orleans, Los Angeles, Memphis and Detroit. Executives said hair damage is also compounded with the use of hot rollers, blowdryers, straight irons and other heated implements, as well as activities such as swimming in pools or the oce...