Two common hookworm infections in humans are ancylostomiasis and necatoriasis, caused by the species "Ancylostoma duodenale" and "Necator americanus" respectively. Hookworm eggs are deposited in the stools of infected people. If these end up in the environment, they can hatch into larvae (immature worms), which can then penetrate the skin. One type can also be spread through contaminated food. Risk factors include walking barefoot in warm climates, where sanitation is poor. Diagnosis is by examination of a stool sample with a microscope.