I recently made the decision to switch from liquid soap to bar soap for personal washing. I was pretty sure bar soap would be more environmentally friendly than liquid soap in plastic bottles. My online research confirmed my hunch but also brought to light another issue that I hadn't even considered.
A 2009 Swiss study found that the carbon footprint of liquids is about 25 percent larger than that of bar soaps on a per wash basis. Liquid soap requires five times more energy to produce and nearly 20 times more energy to package, and, we use about seven times more liquid soap than bar soap for each hand wash. Even though we tend to use about 30 percent more heated water washing with bar soap, it was still the environmental winner.
The environmental issue that I hadn't considered was that traditional bar soaps are made from fats and oils which come from farmed crops that can have a significant environmental impact on land. For example, there are approximately 11 million hectares of oil palm plantations worldwide and in many places these plantations are taking over rainforests, the natural habitat of endangered species such as orangutans. Alternatively, most liquid soaps are made of petroleum based synthetic surfactants which of course come with their own set of environmental impacts.