The hygiene hypothesis is that public health has eliminated many of the pathogens our bodies evolved to fight against, yielding autoimmune diseases (e.g., lupus, diabetes type 1, celiac, Crohn's diseases), allergies and asthma, and other diseases of inflammation because our bodies are used to fighting something so instead attacks itself or benign agents. Someone claims to have cured their asthma by deliberately getting himself infected with hookworms. It's an absorbing and completely ironic travelogue: needing to find disease in the developing world to feel healthy. Others have recovered from Crohn's disease after hookworm infection, and two companies sell hookworm infection. One operates in Mexico just across the US border and gives a bandaid with a hookworm larva on it.