Poisonous substances are materials that can cause harm or illness when they enter the body. These substances can be found in various forms, including liquids, solids, and gases. Common examples include carbon monoxide, lead, and certain plants like poison ivy. Exposure can occur through ingestion, inhalation, or skin contact. The effects of poisonous substances vary depending on the type and amount involved. Symptoms may range from mild irritation to severe health issues or even death. It is important to recognize and avoid these substances, and to seek medical help if exposure occurs. Understanding the risks associated with toxins is crucial for safety.