The LEED program — Leadership in Energy and Environmental Design — is playing an increasingly important role in the drive to make buildings in the United States greener and more energy efficient. LEED is now the most prominent and widely adopted green building certification program in the country, with architects and developers striving to earn LEED’s coveted platinum or gold rating, and an increasing number of local, state, and federal regulations beginning to incorporate LEED standards into official building codes. But LEED — sponsored by the U.S. Green Building Council, an industry group — has a glaring and little-known drawback: It places scant emphasis on factors relating to human health, even as the largely unregulated use of potentially toxic building materials continues to expand. One of LEED's major accomplishments — saving energy by making buildings more airtight — has had the paradoxical effect of more effectively trapping the gases emitted by the unprecedented number of chemicals used in today’s building materials and furnishings.