These days, every skin lotion and dish detergent on store shelves gloats about how green it is. How do shoppers know which are good for them and good for the earth? It was a similar question that hit Dara O'Rourke, a professor of environmental and labor policy at the University of California, Berkeley, one morning when he was applying sunscreen to his young daughter's face. He realized he did not know what was in the lotion. He went to his office and quickly discovered that it contained a carcinogen activated by sunlight. It also contained an endocrine disruptor and two skin irritants. He also discovered that her soap included a kind of dioxane, a carcinogen, and then found that one of her brand-name toys was made with lead. And in looking for the answer, he hatched the idea for a company that used his esoteric research on supply chain management. All I do is study this, and I know nothing about the products I'm bringing into our house and putting in, on and around our family," Mr. O'Rourke said. But when he wanted to find that information, he could. Most consumers would struggle to do so. Hence GoodGuide, a Web site and iPhone application that lets consumers dig past the package's marketing spiel by entering a product's name and discovering its health, environmental and social impacts. GoodGuide's office, in San Francisco, has 12 full-time and 12 part-time employees, half scientists and half engineers. They have scored 75,000 products with data from nearly 200 sources, including government databases, studies by nonprofits and academics, and the research by scientists on the GoodGuide staff.