Worms (intestinal helminths) are parasitic worms that infect the human digestive tract or other tissues, most commonly roundworms (nematodes like Ascaris lumbricoides), hookworms, whipworms, pinworms (Enterobius vermicularis), or tapeworms (cestodes). These infections occur through ingestion of eggs in contaminated soil, food, or water, skin penetration by larvae (e.g., hookworms), or consumption of undercooked meat/fish containing larvae. Many cause no symptoms, but others lead to abdominal pain, diarrhea, nausea, bloating, malnutrition, weight loss, anemia (especially hookworms), itching around the anus (pinworms, often worse at night), visible worms or segments in stool, or coughing/wheezing if larvae migrate through lungs (Ascaris). They are more prevalent in areas with poor sanitation and can affect children disproportionately, sometimes resulting in growth stunting or developmental delays in heavy infections.